KR20040053309A - Radio communication system - Google Patents

Abstract

The wireless communication system has a communication channel for transmission of data packets from a primary station to a secondary station. In operation, when a data packet is detected, the secondary station transmits an acknowledgment signal to the secondary station indicating the state of the received data (408) and resets the timer (406). The secondary station changes the characteristics of the uplink transmission while the timer is running. In one embodiment, the change includes sending a negative acknowledgment every time a data packet could be received if no sign of the data packet was received. In another embodiment the change includes the secondary station changing a parameter related to the transmission of channel quality information to the primary station.

Description

Wireless communication system

In the area of mobile communications, there is an increasing demand for systems having the ability to download large data blocks to mobile stations on demand at a reasonable rate. Such data may be, for example, web pages from the Internet, and may include video clips or the like. In general, certain mobile stations will only occasionally require such data, and such fixed bandwidth only links are not appropriate. To meet the requirements in UMTS, a high speed downlink packet access (HSDPA) scheme has been developed that can facilitate the transmission of packet data up to 4 Mbps to the mobile station.

A conventional component of a packet data transmission system is an automatic retransmission request (ARQ) process for handling received error data packets. For example, consider downlink packet transmission from a base station to a mobile station in HSDPA. When the mobile station receives a data packet, the mobile station determines whether the packet is corrupted, for example using cyclic redundancy check (CRC) information. The mobile station then uses a signal in the field allocated for this purpose as a first acknowledgment (ACK) to indicate that the packet was successfully received and a negative acknowledgment (NACK) to indicate that the packet was received but corrupted. The second signal used as and transmits to the base station. The signals may for example be the same codeword transmitted with different codewords or with different power. The base station requires the proper location of the decision threshold set to enable the accurate decoding of the ACK / NACK messages.

Since packet transmission is generally intermittent, discontinuous transmission (DTX) is generally used so that nothing is sent by the mobile station in the ACK / NACK field if the data packet is not received. In a typical scenario, the mobile station has a 1% chance of failing to detect the sent data packet. In this case, it is preferable that the base station interprets the DTX as NACK so that the packet can be retransmitted to the mobile station. Interpreting DTX as a NACK means that the mobile station transmits a NACK to all ACK / NACK fields that offset the decision threshold at the base station with an ACK signal regardless of whether a packet was detected or does not correspond to a packet with a correct CRC. It can be performed by.

The problem that the mobile station transmits to all ACK / NACK fields is that the uplink interference increases significantly, and in addition, the mobile station battery life is reduced. This is a problem when the packet traffic suddenly explodes (which is often the case), resulting in requiring the mobile station to transmit to many ACK / NACK fields when no packets are sent to the mobile station.

The problem of offsetting the threshold for determining between ACK and NACK commands is that the transmit power of the ACK command needs to be increased (discussed below) to obtain an acceptable low probability that the ACK is interpreted as a NACK. . Since the probability that a mobile station transmits an ACK must be much greater than the probability of transmitting a NACK in a well designed communication system, the increasing ACK transmit power significantly increases the average transmit power required in the ACK / NACK field.

Consider a typical communication system that requires less than 1% probability of misinterpreting an ACK as a NACK, and less than 0.01% as likely to misinterpret an NACK as an ACK. Assuming a 1% probability that the mobile station does not detect a packet, the probability of misinterpreting DTX as NACK should be less than 1% (the combined probability that the mobile station does not detect a packet and misinterprets DTX as NACK is NACK Probability of misinterpreting ACK as ACK, i.e. must be less than 0.01%). Simulations for typical mobile communication channels are sufficient to ensure that the probability of misinterpreting DTX as ACK is less than 1%. Offset a decision threshold toward ACK has the effect of requiring the ACK power greater than the NACK power. Thus, this results in a maximum power requirement for offsetting the base station determination threshold to cause an ACK / NACK field to be determined by the ACK signal other than the NACK signal.

The present invention relates to a wireless communication system and also to a primary station and a secondary station for use in the system and a method of driving the system. Although the detailed description of the invention describes the system in particular with reference to a Universal Mobile Telecommunications System (UMTS), it will be appreciated that the techniques described above are equally applicable to other mobile communication systems.

Embodiments of the present invention will be described with reference to the accompanying drawings.

1 is a block diagram of a wireless communication system,

2 is a view for explaining the operation of the known stop waiting ARQ scheme;

3 is a view for explaining the operation of the known n-channel ARQ scheme,

4 is a flowchart illustrating a method of operating a packet data transmission system according to the present invention.

In the drawings, the same reference numerals are used to indicate corresponding features.

It is an object of the present invention to solve the above identified problems.

According to a first aspect of the present invention, there is provided a wireless communication system having a communication channel for transmitting data packets from a primary station to a secondary station, the secondary station comprising: receiving means for receiving a high data packet and a state of the received data packet Having acknowledgment means for transmitting a signal indicating to the secondary station, the secondary station resets the timer upon detecting an indication that a data packet has been sent to the secondary station, and characteristics of uplink transmissions until the timer expires. Provided is a wireless communication system, comprising means for changing the.

Resetting the timer includes starting the timer if the timer is not yet running, and restarting the timer that is already running. In one embodiment, if no indication of a data packet is detected, the secondary station may be modified to send a negative acknowledgment every time the data packet could be sent. In another embodiment, the secondary station may be modified to change parameters related to transmission of the channel quality information to the primary station. These modifications enable optimization of uplink channel characteristics that depend on uplink interference, maximum power levels and battery life requirements. The timer may be realized as a counter that counts in predetermined units, for example milliseconds, frames, time slots, messages or other suitable units.

According to a second aspect of the present invention, there is provided an apparatus for use in a wireless communication system having a communication channel for transmitting data packets from a primary station to a secondary station, the method comprising: transmitting a data packet to the secondary station and receiving a received data packet. Means for receiving a signal from the secondary station indicating a status, resetting the timer upon receiving an acknowledgment of receipt of a data packet by the secondary station, and changing the processing of uplink transmissions until the timer expires. A primary station is provided, characterized in that it is provided.

According to a third aspect of the present invention, there is provided a receiving station for receiving a data packet from the primary station, the secondary station being used in a wireless communication system having a communication channel for transmitting data packets from the primary station to the secondary station. Acknowledgment means are provided for transmitting a signal indicating the status of a received data packet to the primary station, resetting the timer upon detecting an indication that a data packet has been sent to the secondary station, and when the timer expires. A secondary station is provided, characterized in that means are provided for changing the nature of uplink transmissions.

In another embodiment of the present invention, a timer may also be used to control the period of reporting channel quality information to the primary station.

According to a fourth aspect of the present invention, there is provided a method of operation of a wireless communication system having a communication channel for transmitting data packets from a primary station to a secondary station, wherein the secondary station receives a data packet and indicates a state of received data. Transmitting to the primary station, the secondary station resetting the timer upon detecting an indication that a data packet has been sent to the secondary station, and changing the characteristics of uplink transmissions until the timer expires. An operating method is provided, characterized in that

Referring to FIG. 1, a wireless communication system includes a primary station (BS) 100 and a plurality of secondary stations (MS) 110. The primary station 100 is a microcontroller (μC), a transceiver (Tx / Rx) 104 connected to the antenna 106, a power control means (PC) 107 for changing the transmitted power level, and a PSTN or other. Connection means 108 are provided for connection to the appropriate network. Each MS 110 has a microcontroller (μC) 12, a transceiver (Tx / Rx) 114 connected to an antenna 116, and a power control means (PC) 118 for changing the transmitted power level. Equipped. Communication from BS 100 to MS 110 takes place in downlink channel 122, while communication from MS 110 to BS 100 occurs in uplink channel 124.

An example of the operation of the known stop waiting ARQ scheme is shown in FIG. 2. Packets 202 identified by data Pn (n is a one-bit sequence number) are transmitted on downlink channel DL from BS 100 to MS 110 in the assigned time slot. Sequence number The first data packet P ₀ of 0 is received by the MS (100) to a state with errors, so that the MS (100) has confirmed no reception in the field reserved for transmission of positive and negative acknowledgment ( N) 204 is transmitted. In response, the BS 100 retransmits the first data packet 202, whereby the first data packet 202 is correctly received by the MS 100 sending an acknowledgment (A) 206. FIG. do. The BS 100 then transmits the next packet with sequence number one. The BS 100 retransmits the data packet 202 if no acknowledgment is received within the predetermined time elapsed period (the MS 110 has not received the packet at all or the acknowledgment is lost). If the MS 110 actually receives the previously transmitted packet 202, the MS 110 determines whether the received packet 202 is retransmitted because the received packet has the same sequence number as the previous packet. Can be.

Improved throughput can be obtained using multi-channel ARQ schemes. An example of a four-channel ARQ scheme operating in a known manner is shown in FIG. 3. Packets 202 identified with data Pn (n is an order number) are transmitted in sequence on downlink channel DL from BS 100 to MS 110. Each packet 202 is assigned a logical channel CH, starting from the first packet. Thus, the packet P _1, the channel 1 is assigned, the packet is P _2, the assigned channel 2. ARQ is performed independently for each channel.

In the scenario described above, a first data packet P ₁ is sent over a first logical channel and correctly received by the MS 110, which sends an acknowledgment (A ₁ ) 206 to the uplink channel 124. ) To send. Thus, when channel 1 is next reserved for transmission, the next packet P5 waiting for transmission is selected and transmitted to the MS 110. Similarly, a second data packet P2 is sent over the second logical channel. However, this packet is not correctly received by the MS 110 and the MS 110 issues a negative acknowledgment (N2) 204. Thus, when channel 2 is next reserved for transmission, packet P2 is transmitted again. This time packet P2 is correctly received and an acknowledgment 206 is issued on the uplink channel 124 to free channel 2 to transmit other packets 202.

DTX is likely to be justified in the ACK / NACK field for large amounts of time given the typical intermittent nature of packet data transmission. In addition, for a well designed system, NACKs 204 should be sent significantly less frequently than ACKs 206. However, as discussed briefly above, there are problems associated with adjusting the BS 100 to interpret the DTX as a NACK.

These problems are solved by adjusting the MS 110 to operate in two states, a first state where packet transmissions are expected and a second state where packet transmissions are not expected, in a system built in accordance with the present invention. The transition between these two states is controlled by a timer. The timer is typically realized as a counter that counts in certain units, such as milliseconds, frames, time slots, messages or other suitable units.

The operation of such a system is described with reference to the flow chart shown in FIG. The method begins at step 402 when the MS 110 is ready to receive data packets 202. Test 404 involves MS 110 determining whether the data packet was transmitted within a time slot within which the data packet can be transmitted. If a data packet 202 is detected, the test 404 is passed, the timer is reset in step 406, an acknowledgment 206 is sent in step 408, and the MS 110 returns to the test 404 to send the data packet ( Check next appropriate slot for 202). Resetting the timer means starting the timer or restarting a timer that is already running if the timer is not yet running.

If no packet is detected, the test 404 fails and another test 410 is made to determine if the timer is running. If the timer is running, the test 410 passes and the MS 110 sends a negative acknowledgment 204 to the corresponding ACK / NACK field in step 412 and then returns to test 404. If the timer is not running, test 410 fails and MS 110 directly returns to test 404.

The MS 110 assumes that a packet can be sent to itself in any time slot, or after a packet 202 has been received while no packet can be sent to it (much shorter than the duration of the timer). Can be assumed, so the MS will not transmit in the ACK / NACK field. If the timer has stopped, the MS 110 stops transmitting to the ACK / NACK field until the next packet 202 is detected.

This approach allows the BS 100 to adjust its decision threshold so that the transmit power of the MS 110 is optimized. In one embodiment of the invention, the BS 100 offsets its decision threshold toward the ACK signal for the first packet P ₀ of the sequence, increasing the probability that the DTX is interpreted as NACK. This also has the effect of increasing the probability that the ACK 206 of the first packet is interpreted as a NACK 204. As soon as the BS 100 detects the ACK 206 for the first packet P ₀ , the threshold for subsequent decisions is reversed back towards the DTX level, and the BS 100 resets the MS 110. Activates its own timer corresponding to the timer in operation.

As a result, the problem of interpreting DTX as ACK 206 can be avoided for all packets 202 except for the first P ₀ in each sequence, reducing interference or reducing cell range or battery life on demand. It is possible to allow the ACK / NACK power levels to be optimized to increase.

In one embodiment of the present invention, the average power requirement for the ACK / NACK field is minimized. This may be useful in systems where it is desirable to maximize battery life of the MS 110 or minimize uplink interference. In this embodiment, the decision threshold moves closer to the DTX level with the decrease in the ACK power and the increase in the NACK power. Our pending unpublished UK patent application 0126421.7 (applicant reference PHGB 010185) can control the relative probability of error in decoding ACKs and NACKs by changing their relative transmit powers applicable in this embodiment. have.

In another embodiment of the present invention, the maximum power requirement for the ACK / NACK field is minimized. This may be useful in systems where the cell range for packet access is limited by the maximum power requirement for the ACK / NACK field. In this case, the AC and NACK transmit power will be set equally, and the threshold at the BS 100 will be located to give the required error rates.

In a preferred embodiment of the present invention, the MS 110 increases the transmit power of the first ACK 206 in the sequence so that the probability of misinterpreting the ACK as NACK is applied by the BS 100. It is not incremented by the offset in the decision threshold for packet P ₀ .

In another preferred embodiment of the present invention, the timer operates during any number of time slots where no more packets are sent to the MS 100. During this period, ACKs 206 and NACKs 204 are repeated every time slot as appropriate. If the timer stops, the transmission of ACKs 206 also stops (the MS 100 failed to detect the next packet but the BS 100 failed to detect that the MS 110 correctly received the packet. To avoid sending ACKs of trusting results).

In practice, it is desirable to limit the maximum number of repeated NACKs 204 to limit interference and reduce transmit power. This limit may be determined by a second timer and the maximum value of the second timer may be predetermined or set according to a higher layer parameter known by the BS 100 as a signal, or the BS 100 and the MS ( 110). In general, the second timer is set to stop after the transmission of a specified number of NACKs. The use of such a restriction has the advantage that the BS 100 knows how long to wait before determining whether a packet has been correctly received. The second timer may have a different value from the timer, and may count in different units if necessary.

This embodiment can also be used with other embodiments in which different power levels are set for the ACK and NACK signals. The BS 100 may determine whether the ACK 206 or NACK 204 was sent by a variety of methods including coherent combination of multiple ACK / NACK repetitions, selection of the strongest signal, and majority of received signals. Can be. It can dynamically adjust its decision threshold according to the number of ACK / NACKs processed to obtain a specified quality of service.

If the MS 110 sends the ACK 206 as repeatedly as possible, the next action returns to sending DTX after the last ACK, or sending NACKs until the next packet is received or the NACK timer expires. It can be any one of going. Since the latter can prevent transmission of the DTX state, preventing the BS 100 from offsetting its decision threshold and allowing the power for ACK transmission to be reduced (increasing indirect level and MS 110 power consumption). Although the latter should also be considered), the latter choice is generally preferred.

The present invention can be applied to aspects of uplink signaling other than NACK signals. In its most general form the technique relates to a change in the characteristics of uplink signaling depending on whether a packet has been detected during a predetermined period prior to the signaling.

As an example of this more general applicability, in another embodiment of the present invention, the MS 110 makes changes to the transmission of channel quality information (CQI) depending on the likely expectation of packet reception. CQI can be determined by measuring the channel quality of the downlink, for example, by a signal-to-interference ratio (SIR). Changes in CQI transmission include not only the transmission format (bit number) used and the transmission power level, but also a change in the frequency at which CQI is transmitted. For example, the MS 110 may transmit a CQI in all CQI fields available for a period of time determined by a timer after the packet is received. After a predetermined period of time, the MS 110 may decrease the frequency of transmitting the CQI until another packet 202 is received.

In one embodiment where a change is made to both NACK and CQI signaling, the timer used to control the frequency reporting the CQI and the timer used to control the NACK transmission may be the same or may have different values. . These values may be predetermined (eg, at the capacity of the MS), or may be signaled to the MS 110 by higher protocol layers.

The above discussion relates to determining whether the MS 110 has received the packet 202. In some embodiments, for example UMTS, the presence of a packet destined for the MS 110 is signaled by a packet indicator message on a control channel and / or packet indicator channel different from the packet transmission channel. In such an embodiment, a trigger that activates the timer may require accurate decoding of the associated downlink control channel (including CRC) in addition to the detection of a packet indicator. This helps to prevent pseudo triggering of the timer by false detection of the packet indicator.

In our ongoing unpublished international patent application PCT / IB02 / 02834 (applicant reference PHDE 010247), a physical layer mechanism is disclosed which recovers from the case where the BS misinterprets the NACK 204 as an ACK 206. This mechanism uses an additional code word 'REVERT' to inform the BS 100 that the MS 110 has received a transmission of a new packet 202 when it is expecting a retransmission of a previous packet. In this scheme change, two REVERT code words are used to provide additional NACK or ACK for new packets. The present invention can be used with such a REVERT command that can be signaled using the power offset from the NACK command as disclosed in GB0126421.7.

In another embodiment of the present invention, when the MS 110 operates in the first state (when packet transmission is described), it is determined that two different levels of NACK 204 depend on whether a packet indicator has been detected. Can transmit For example, if no packet indicator is detected, the MS 110 transmits a low power NACK 204 such that the probability that the NACK is incorrectly interpreted as an ACK is 1% (this means that the MS 110 receives the With a 1% probability of not receiving a packet indicator, the BS 100 gives a 0.01% probability of interpreting a NACK as an ACK). If a packet indicator is detected, the MS 110 transmits a high power NACK 204 such that the probability that the NACK is incorrectly interpreted as an ACK is 0.01%. These other kinds of NACKs can also be distinguished by the transmission of other code words.

In another embodiment, the operation of uplink power control is changed by the detection of the packet until the timer expires. In a soft handover state in which the MS 110 can receive simultaneous transmissions from one or more BSs 100 (number of active sets), the power of the uplink transmission is generally all BSs locators in the active set. Is controlled by taking into account power control commands. However, if a downlink packet is sent from one particular BS, all uplink signaling in response to that packet must be directed to that BS. Thus, in order to obtain adequate power for that radio line, the power of the uplink transmission must be determined first by the power control commands from the BS. Therefore, when a packet is received from a given BS 100, a timer is set and the power of at least one of the ACK / NACK field, the CQI field or the entire control channel is the power from the same BS until the timer expires. Determined by control commands. If the next packet is received from another BS, the timer is reset and the BS controls the uplink power levels. This change to uplink power control may occur independently or in conjunction with other changes to ACK / NACK or CQI transmissions, as discussed above.

The above description has focused on UMTS Frequency Division Duplex (FDD) mode. The present invention is also applicable to the time division duplex (TDD) mode. In this case, the fact that the uplink and downlink channels use different time slots (ie, reversible channels) at the same frequency can reduce the need for signaling of channel information.

The above description relates to the BS 100, which plays various roles in connection with the present invention. In practice, these tasks may be the responsibility of various components at a higher level in a fixed node, for example, a "Node B" or radio network controller (RNC) that is part of a fixed infrastructure that interfaces directly with the MS 110. Can be. Therefore, in this specification, the use of the term 'base station' or 'primary station' may be interpreted as including the parts of the network fixed infrastructure included in the present invention.

From the disclosure of the present invention, other changes may be apparent to those of ordinary skill in the art. Such changes may include features already known in the design, manufacture, and use of wireless communications systems and their components, and may be used instead of or in addition to the features already described herein.

In the present specification and claims, the word “a” or “an” before an element does not exclude the presence of a plurality of such elements. In addition, the word "comprising" does not exclude the presence of elements or steps other than those described.

Claims (19)

A wireless communication system having a communication channel for transmitting data packets from a primary station to a secondary station, the system comprising: The secondary station has receiving means for receiving a data packet and acknowledgment means for transmitting a signal indicating the state of the received data packet to the primary station, The secondary station comprises means for resetting a timer upon detection of an indication that a data packet has been sent to the secondary station, and for changing the characteristics of uplink transmissions until the timer expires. The method of claim 1, The transmission indication of the data packet is transmitted in a channel different from the channel used for transmission of the data packet. A primary station for use in a wireless communication system having a communication channel for transmitting data packets from a primary station to a secondary station, Send a data packet to the secondary station, receive a signal from the secondary station indicating the status of a received data packet, reset the timer upon receipt of the acknowledgment of the data packet by the secondary station, and when the timer expires Means are provided for modifying the processing of uplink transmissions until. The method of claim 3, wherein If a data packet was not sent, receive a negative acknowledgment every time the data packet could be sent to a secondary station, set a threshold for determining whether the received signal is a positive or negative acknowledgment, and the timer expires. Means for setting the threshold to a different value while the timer is operating in comparison with the value used after the operation has occurred. The method of claim 4, wherein Means for setting a threshold closer to the positive acknowledgment signal than the negative acknowledgment signal after the timer expires and a packet has been sent to the secondary station. Said secondary station for use in a wireless communication system having a communication channel for transmitting data packets from a primary station to a secondary station, Receiving means for receiving a data packet from the primary station is provided, acknowledgment means for transmitting a signal indicative of the status of a received data packet to the primary station is provided, and an indication that a data packet has been sent to the secondary station is provided. Means are provided for resetting a timer upon detection and for changing the nature of uplink transmissions until the timer expires. The method of claim 6, Means for delaying the reset of the timer until another indication of transmission of the data packet containing error correction information is successfully received. The method according to claim 6 or 7, If no transmission of the data packet is detected, means are provided for sending a negative acknowledgment every time the data packet could be transmitted, and only such negative acknowledgments are transmitted until the timer expires. Secondary station made with. The method according to claim 7 or 8, And means for transmitting an acknowledgment of the first packet received after expiration of the timer at a higher power than the acknowledgment of subsequent packets while the timer is running. The method according to any one of claims 7 to 9, And a means for transmitting positive and negative acknowledgments at about the same power. The method according to any one of claims 7 to 9, When the indication of transmission of the data packet is not detected, the indication for transmission of the data packet is received at the first low power, but when the indication of the transmission of the data packet is received correctly but the data packet is not correctly received, a second acknowledgment for transmitting a negative acknowledgment. Secondary station, characterized in that means are provided. The method of claim 6, Means are provided for acknowledgment that the data packet has been sent to reset another timer, and means for repeating positive acknowledgments until the timer expires, and negative receipt until the other timer expires. And a means for repeating the checks. The method of claim 12, The duration of the other timer is greater than the duration of the timer. The method according to any one of claims 8 to 13, And the available signal types further comprise a return signal indicating a retransmission request of the received packet prior to the most recently received packet. The method according to any one of claims 6 to 14, And means for changing a parameter associated with the transmission of channel quality information to said primary station while said timer is running. The method of claim 15, The parameter is at least one of a transmission rate at which channel quality information is transmitted to the primary station, a format of channel quality information transmitted to the primary station, and a power at which channel quality information is transmitted to the primary station. . The method according to claim 15 or 16, And the timer associated with the transmission of negative acknowledgments and the timer associated with the transmission of channel quality information are identical. The method according to any one of claims 6 to 17, Means are provided for communicating with a plurality of primary stations at substantially the same time, receiving power control commands from each of the primary stations, and receiving a data packet from any of the primary stations, while the timer is running. Means for setting power of uplink transmissions in accordance with power control commands received from the primary station transmitting the packet and power control commands received from all the primary stations when the timer expires. Secondary station made with. A method of operation of a wireless communication system having a communication channel for transmitting data packets from a primary station to a secondary station, the method comprising: The secondary station receiving a data packet and transmitting an acknowledgment signal to the primary station indicating the status of the received data packet, The secondary station resets a timer upon detection of an indication that a data packet has been sent to the secondary station and changes the characteristics of uplink transmissions until the timer expires.