KR100975310B1 - Communication system using arq - Google Patents

Abstract

The communication system transmits and receives a downlink data channel for transmitting data packets from a primary station to a secondary station and status signals. And a second channel for transmitting pilot information and a second channel for transmitting pilot information. In operation, if a data packet is detected (402), the secondary station increases the transmit power of the second channel (404), thereby causing the primary station to obtain a better estimate of the uplink channel characteristics, thereby providing a status signal. It can increase the accuracy of decoding (status signal). The secondary station typically transmits a status signal of either an acknowledgment (ACK) or a negative acknowledgment (NACK) (406) and reduces the transmit power of the second control channel signal. (408). For example, the increase and decrease of the output by the effect of the output control need not necessarily be the same.

Description

Communication system and primary and secondary station and communication system driving method used therein {COMMUNICATION SYSTEM USING ARQ}

The present invention relates to a communication system, a primary station and a secondary station used in such a system, and a method of operating such a system. In the specification of the present invention, in particular, a system related to a universal mobile telecommunication system (UMTS) has been described, but it will be understood that this technique can be equally applied to other communication systems.

In the field of mobile communications, there is an increasing need for a system having the ability to download large amounts of data to mobile stations (MSs) at moderate rates on demand. Such data may be, for example, web pages on the Internet that may contain video clips or the like. Typically, fixed bandwidth dedicated links are not appropriate because a particular MS will only need this data intermittently. To meet these requirements with UMTS, a high-speed downlink packet access (HSDPA) technique has been developed that can transmit packet data to mobile stations at speeds of at least 4 Mbps.

Conventional components of a packet data transmission system include an Automatic Repeat reQuest (ARQ) process, which is intended to process incorrectly received data packets. For example, consider downlink packet transmission from a base station (BS) to a mobile station (MS) in HSDPA. When the MS receives the data packet, it determines, for example, whether the packet is damaged by using cyclic redundancy check (CRC) information. The MS then sends a signal in the field allocated for this purpose to the BS, where the first signal is used as an acknowledgment (ACK) indicating that the packet was successfully received, and the second signal is received by the packet. It is used as a negative acknowledgment (NACK) to indicate that it is damaged but damaged. These signals may be, for example, different codewords or the same codeword transmitted to different outputs.

In the technique defined herein for HSDPA, a number of channels are defined, each channel processing a different type of information, which will be described only in connection with the present invention. Data packets are sent on the (high speed) downlink data channel in the direction from the BS to the MS and on the uplink data channel in the opposite direction. Two uplink control channels are defined for signal transmission by the mobile device. The transmission of the ACK / NACK message is performed on a first uplink control channel (HS-DPCCH), while pilot information of pilot information for causing the BS to obtain a channel estimate of the uplink channel. The transmission is performed on a second uplink control channel (DPCCH). The output level of the second control channel is set by the BS using closed loop power control. The output level of the uplink data channel is determined by the output of the second control channel. The ratio of these two output levels can be determined by a gain factor, a value that can be delivered to the MS, or independently by the MS.

The consequences of errors in the ACK message and the NACK message are quite different. In general, the BS retransmits a packet when a NACK is received. If an ACK was sent but the BS received a NACK, the packet is retransmitted once. It only consumes small system resources. If the NACK is transmitted but the BS receives the ACK, no retransmission occurs. Without a special physical layer mechanism, this situation can only be restored by a higher layer process, which adds time delays and consumes significant system resources. Therefore, the effect by error in NACK is much more severe than the effect by error in ACK, so the performance condition in 3GPP is set to 10 ⁻² in case of ACK error and 10 ⁻ in case of NACK error. ^Is set to ⁴ . Good channel estimation is necessary to achieve these error rates. In particular, in the case of using phase modulation (e.g., BPSK or QPSK, etc.), a data channel phase is required in order to accurately determine the phase of data symbols. For modulation schemes where amplitude is also an important variable, such as m-QAM (eg m is 16), channel amplitude will also be needed.

It is an object of the present invention to satisfy the need for good channel estimation.

According to a first aspect of the invention, a downlink data channel for transmitting a data packet from a primary station to a secondary station and a first for transmitting information related to the reception of the data packet from the secondary station to the primary station A communication system is provided that includes an uplink control channel and a second uplink control channel for transmitting pilot information, the secondary station comprising receiving means for receiving data packets and a primary station on the first control channel. Verifying means for transmitting the status signal to indicate the status of the received data packet, wherein the secondary station transmits a transmission output for at least a portion of the second control channel containing pilot information during a predetermined period of time for transmitting the status signal. And an output control means for temporarily increasing.

Temporary increases in the transmit output of the pilot signal can improve channel estimation, thereby improving the accuracy of ACK / NACK message detection without significantly increasing the overall interference level. The increase in output at the beginning of the temporarily increased output period will be different from the decrease in output at the end of that period, for example as a result of the inner-loop power control operation.

According to a second aspect of the invention, a downlink data channel for transmitting a data packet from a primary station to a secondary station, and a first for transmitting information related to reception of the data packet from the secondary station to the primary station A primary station for a communication system is provided that includes an uplink control channel and a second uplink control channel for transmitting pilot information, the primary station indicating a state of a data packet transmitted to the secondary station. Means for receiving a signal on a first control channel, a closed loop output control means for controlling the output of an uplink control channel, and a pilot information comprising pilot information due to the transmission of status signals by the secondary station. 2 Near the time expected to take into account the transient increase in transmit power for at least a portion of the control channel. Adjustment means are provided for adjusting the operation of the output control means for a predetermined period.

According to a third aspect of the invention, a downlink data channel for transmitting a data packet from a primary station to a secondary station, and a first for transmitting information related to reception of the data packet from the secondary station to the primary station A secondary station is provided for a communication system comprising an uplink control channel and a second uplink control channel for transmitting pilot information, the secondary station comprising: receiving means for receiving data packets from the primary station; Confirming means for indicating a state of the received data packet by transmitting a status signal on the first control channel to the primary station, and transmitting output of at least a portion of the second control channel including pilot information during a predetermined period of time during which the status signal is transmitted. And an output control means for temporarily increasing.

According to a fourth aspect of the invention, a downlink data channel for transmitting a data packet from a primary station to a secondary station and a first for transmitting information related to reception of the data packet from the secondary station to the primary station A method of driving a communication system having an uplink control channel and a second uplink control channel for transmitting pilot information is provided, the method comprising: receiving a data packet using a secondary station; Transmitting a status signal to a primary station on the signal indicating the status of the received data packet, wherein the secondary station comprises at least a portion of the second control channel containing pilot information for a predetermined period of time during which the status signal is transmitted. Temporarily increases the transmit power for.

Next, by way of example, embodiments of the invention will be described with reference to the accompanying drawings.

Like reference numerals have been used to designate like features in the figures.

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

2 illustrates the operation of a known stop-and-wait ARQ technique;

3 is a diagram illustrating operation of a known n-channel ARQ scheme;

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

Referring to FIG. 1, a wireless communication system includes a primary station (BS) 100 and a plurality of secondary stations (MS) 110. BS 100 is a microcontroller (μC) 102, transceiver means (Tx / Rx) 104 connected to antenna means 106, and output control means (PC) 107 for changing the transmitted output level. ) And connecting 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 an antenna means 116, and an output control means (PC) for changing the transmitted output 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.

An example of the operation of the known stop-and-wait ARQ technique is shown in FIG. 2. Data packet 202, denoted by P _n (n is a 1-bit sequence number), is transmitted in allocated time slots on downlink data channel (DL) 122 from BS 100 to MS 110 do. The first data packet P ₀ with sequence number 0 is received at the MS 110 in a corrupted state, and thus a negative response (N) with a field reserved for the transmission of a positive and negative response on the first uplink control channel. 204). In response, BS 100 retransmits first data packet 202, which is then received by MS 110 sending a positive response (A) 206. BS 100 then transmits the next packet with sequence number one. In addition, if no acknowledgment was received during the predetermined time-out period (if MS 110 did not receive the packet, or if the acknowledgment was lost), BS 100 receives the data packet 202. Resend). If the MS 110 actually received the previously transmitted packet 202, it may decide to retransmit since the received packet 202 has the same sequence number as the previous packet.

By using a multi-channel ARQ technique, improved throughput can be obtained. An example of a four-channel ARQ technique that works in a known manner is shown in FIG. 3. The data packet 202, denoted by P _n (n is a 1-bit sequence number), is sequentially transmitted from the BS 100 to the MS 110 on the downlink channel (DL) 122. Each packet 202 is assigned sequentially to the logical channel CH starting from the first packet. Thus, packet P ₁ is assigned to channel 1 and packet P ₂ continues in such a way that channel 2 is assigned. ARQ is executed separately for each channel.

In the illustrated scenario, the first data packet P ₁ is transmitted over a first logical channel and correctly received by the MS 110, where the MS 110 receives an acknowledgment A ₁ 206. ) On the uplink channel 124. Thus, when channel 1 is next scheduled for transmission, it selects the next packet P _{5 that} is waiting to be transmitted and transmits to MS 110. Similarly, the second data packet P ₂ is transmitted on the second logic channel. However, this packet is not correctly received by the MS 110 and the MS 110 issues a negative response (N ₂ ) 204. Thus, when channel 2 is next scheduled for transmission, it transmits packet P ₂ again. At this point, the packet P ₂ is correctly received and an acknowledgment 206 is issued on the uplink channel 124, allowing the channel 2 to be ready to transmit another packet 202.

As mentioned above, good channel estimation is necessary for the BS 100 to achieve the level of accuracy required to decode the ACK / NACK message. Channel estimation is performed by receiving pilot information transmitted on a second uplink control channel, in a known manner. The output level of the second uplink control channel is generally set to provide the correct output level for the uplink data channel in accordance with the relative gain factor between the two channels. In this case, however, the output level set for the second uplink control channel will not be high enough to enable channel estimation that is good enough to reliably detect ACK / NACK messages simultaneously.

In a system formed in accordance with the present invention, this problem is solved by temporarily increasing the output of the second uplink control channel (or at least a portion of that channel containing pilot information) when an ACK / NACK message is sent. Can be. After sending the message, the output level is reduced by the same amount.

The operation of this system will be described with reference to the flowchart shown in FIG. This method begins at step 402 by the MS 110 detecting the downlink data packet 202. In response to this detection, MS 110, step 404, increases the transmit power of the second control channel by a predetermined amount. Next, the MS 110 determines, as step 406, whether the data packet was received correctly and sends the ACK 206 or NACK 204 as appropriate. Finally, at step 408, MS 110 reduces the transmit power of the second control channel by a predetermined amount, which is not necessarily the same amount as the increased output at step 404. An example of a case where these amounts are required to be different is a system in which a temporary increase in output at the beginning and end of a period occurs simultaneously with (and in combination with) this regular inner loop output control phase. There is this. The output control step is likely to be opposite directions at the beginning and end of the period, which causes the amount of increase and decrease of the output to be different from each other.

In the HSDPA embodiment, the presence of a packet to be transmitted to the MS 110 is signaled by a packet indicator message on a packet indicator channel and / or control channel separate from the packet transport channel. do. In this embodiment, the trigger for increasing the transmit power of the second control channel requires, in addition to the detection of a packet indicator, accurate decoding of the associated downlink control channel (including CRC). Shall be. This makes it possible to avoid spurious triggering of the timer due to false detection of the packet indicator.

If a packet indication message is detected, then an increase in output may be applied at the beginning of a slot in the second uplink control channel just prior to the time scheduled to transmit the ACK / NACK message on the first uplink control channel. Subsequently, following the transmission of the ACK / NACK message (or optionally the next transmission), the output increase can be eliminated at the end of the slot. Such an apparatus may send one or more sets of pilot symbols at a higher output level, which helps the BS 100 track channel variations. However, ideally the duration of the increased transmit power should always include at least one pilot field (including a complete set of pilot symbols or bits). It should be noted that the first and second uplink control channels do not have the condition that their slots must be aligned (or have the same duration). Similarly, applying output variability to slot boundaries was particularly useful for HSDPA but is not necessary here.

The output increase may be defined as an output offset relative to the normal output level of the second uplink control channel, which in turn has a positive value. In this case, the BS 100 is aware of the rules used by the MS 110 to apply the output offset and can modify the output control operation (if necessary) accordingly, thus regulating the regular output of this channel. The operation can be applied after the offset has been applied or removed. However, there is a problem here that BS 100 does not necessarily have complete knowledge of whether the mobile device uses an offset (since it depends on the detection of data packets).

Variations within any range of the basic techniques described above can be made. For example,                 

The output offset can be fixed for all mobile devices or a signal can be sent for the mobile device. When a signal is sent, this signal transmission is carried out over a regular signal channel or, in the case of HSDPA, over a High Speed Shared Control CHannel (HS-SCCH), which updates the output offset in response to fluctuations in channel conditions. Make it faster

Different output offsets may be applied for the ACK 206 and NACK 204 messages. However, additional delay will be incurred before recognizing the packet state. The choice of output offset can represent a balance between performance and interference.

If the output offset is signaled, the value may be determined according to a predetermined detection threshold at the BS 100.

To keep the reliability of the ACK / NACK message substantially constant, it is desirable to simultaneously update the output offset and other parameters (e.g., the number of repetitions of the ACK / NACK, etc.).

The output offset can be changed during the period in which the output is increased (eg it starts with an initial value and can be changed when recognizing the packet state).

The duration of the output offset can be set by a timer starting at the point in time at which the data packet was detected or received. Such a timer may be implemented as a counter that counts in predetermined units such as milliseconds, frames, time slots, messages or other suitable units.

Any output offset applied in accordance with the present invention may be applied in addition to the output offset determined by other mechanisms, such as output variations signaled to MS 110 or variations made for purposes other than those mentioned herein. have.

As a more specific example for UMTS HSDPA, the reliability of ACK / NACK may be improved by repetition of the ACK / NACK message. However, sending more data packets during the repetition period may not be allowed, which may limit the obtainable bit rate. Therefore, if the required bit rate is increased, it will be necessary to reduce the number of repetitions of ACK / NACK. In order to keep the overall reliability of ACK / NACK the same, an output offset may be applied simultaneously to increase the output of the DPCCH or the output of the HS-DPCCH (delivering ACK / NACK) to the DPCCH. If such a signal is carried on the HS-SCCH, it is desirable to reduce the total number of bits used. If two bits are allocated, four different combinations can be signaled, as shown in the following table.

This variation may be for a predetermined value and the higher layer signal for the current value. The output offset value mentioned herein may be applied to the DPCCH or HS-DPCCH depending on the embodiment. Some restrictions may be imposed on the maximum and minimum values, especially when the variation relates to the current value. The maximum number of ACK / NACK transmissions is explicitly limited to one. If only one bit can be signaled, only two combinations may be used, for example in the following table.

If the duration of the output offset is more than a small number of slots, then a modified output control operation can be considered. Any output offset may be applied over the same time period as it is applied. As a specific example, the output control taken by the MS 110 in a UMTS soft handover (the MS 110 communicates with two or more base stations 100, known as an active set). The task is derived by considering output control commands sent from all base stations in the active set. In a system formed in accordance with the present invention, it preferentially takes into account output control commands sent from the MS 100 or from the BS 100 (the BS 100 also sends data packets during the modified output control operation). It can be modified to.

As described above, the output level of the uplink data channel is determined by the output level of the second control channel set by the BS using closed loop output control. The ratio of these two output levels is determined by a gain factor A that can be signaled to the MS 110 or independently determined by the MS. While the output increase is applied, the gain factor can be recalculated to keep the output level of the uplink data channel constant (relative to the target level). This is desirable in that it avoids generating additional interference or affecting the quality of the data transmitted on the data channel.

In UMTS FDD mode, the uplink target (SIR) (applied to the pilot field on the uplink DPCCH) may be signaled from the Radio Network Controller (RNC) to the BS 100 (or Node B). have. This mechanism can be used to improve ACK / NACK reliability by increasing the DPCCH output for a long time, even at the expense of increased interference. The method of the present invention is advantageous because it provides an additional signal to inform node B of the magnitude of any temporary output offset to be applied to the target SIR when ACK / NACK is sent by MS 110. Do. Suitable values of the offset may be, for example, 0, 2, 4 or 6 dB, and the like.

One possible embodiment is applicable to the present invention only when the MS 110 is not in soft handover. In the soft handover state (ie, when the MS 110 communicates with one or more BSs), the existing higher layer signal can be used to increase the DPCCH output for a long time.

In UMTS, mechanisms for defining and obtaining gain parameters and resulting gain coefficients are already defined. In the system formed according to the present invention, when the output offset is applied to the second control channel, in order to keep the output level of the uplink data channel at the same level as when no output offset is applied to the second control channel, a new gain You need to determine the parameters and get their values. One way to do this is to calculate the gain factor (A) according to the following equation.

Here, β _d is a gain parameter applied to the uplink data channel, β _c is a gain parameter applied to the second uplink control channel, and Δ = 10 ^{δ / 20} , where δ is an additional output applied to the second control channel. Offset in dB. In the current UMTS specification, the gain parameter has a value between 0 and 1, and at each step has a value of 1/15. Applying this implementation, one embodiment of the present invention can be operated as follows.

If A> 1, then set a new value such that β _d = 1 and β _c are the gain coefficients obtained as maximum values at β _c ≦ 1 / A.

If A ≦ 1, then set a new value such that β _c = 1 and β _d are the gain coefficients obtained as minimum values at β _d ≧ A.

A similar modification is necessary for the set of gain coefficients and gain parameters if Δ indicates a decrease in output after the ACK / NACK message is sent.

The operation of the present invention may be controlled (eg, enabled, modified or disabled) by a particular signaling message. In addition, such control can potentially be performed depending on the parameter value signaled for other purposes. For example, if the operation of the present invention is controlled by analysis of a predetermined number of output control commands K, the operation can be disabled by BS 100 signaling a value of K as zero. .

The same approach as described above can be used to improve the reliability of other signals transmitted on the first control channel, for example Channel Quality Information (CQI). The output offset used for other signals may be different than the output offset used for ACK / NACK messages.

The foregoing is directed to a downlink data channel in UMTS Frequency Division Duplex (FDD) mode. In addition, the present invention can be applied to a time division duplex (TDD) mode and an uplink data channel.

The foregoing is directed to a BS 100 for performing various tasks related to the present invention. In practice, this task may involve a number of parts of the fixed infrastructure, for example, "node (B)" which is part of a fixed infrastructure that is directly connected to the MS 110, or a radio network controller (RNC) at a higher level. And so on. Therefore, in this specification, the term "base station" or "primary station" should be understood to include part of a network fixed infrastructure included in embodiments of the present invention.

Other modifications will become apparent to those skilled in the art upon reading this specification. Such modifications may include other features that are already known in the design, manufacture, and use of communication systems and their components, and that may be used in place of or in addition to the features already described herein.

Claims (13)

As a communication system, A downlink data channel for transmitting data packets from a primary station to a secondary station, A first uplink control channel for transmitting information related to receiving the data packet from the secondary station to the primary station; Second uplink control channel for transmitting pilot information ≪ / RTI > The secondary station, Receiving means for receiving the data packet; Confirmation means for indicating a status of a received data packet by transmitting a status signal to the primary station via the first uplink control channel; Output control means for temporarily increasing a transmission output for at least a portion of said second uplink control channel comprising said pilot information during a predetermined period during which said status signal is transmitted; Communication system comprising a. Primary stations used in communication systems, The communication system, A downlink data channel for transmitting data packets from the primary station to the secondary station; A first uplink control channel for transmitting information related to receiving the data packet from the secondary station to the primary station; Second uplink control channel for transmitting pilot information Including, The primary station, Receiving means for receiving a status signal indicative of the status of the data packet transmitted to the secondary station via the first uplink control channel; Closed loop output control means for controlling the output of said first uplink control channel and said second uplink control channel; The closed loop in view of a temporary increase in transmit power for at least a portion of the second uplink control channel containing the pilot information during a predetermined period near the time at which transmission of the status signal by the secondary station is expected. Adjusting means for adjusting the operation of the output control means Primary station comprising a. The method of claim 2, Means for signaling to the secondary station the magnitude of the transmit power increase that should be applied. The method of claim 3, wherein Means for signaling a change in another parameter to the secondary station simultaneously with the magnitude of the transmit power increase being signaled to the secondary station. The method of claim 4, wherein Said other parameter being the number of repetitions of said status signal. Secondary station used in communication systems, The communication system, A downlink data channel for transmitting data packets from the primary station to the secondary station; A first uplink control channel for transmitting information related to receiving the data packet from the secondary station to the primary station; Second uplink control channel for transmitting pilot information ≪ / RTI > The secondary station, Receiving means for receiving the data packet from the primary station; Confirmation means for transmitting a status signal to the primary station via the first uplink control channel, the status signal indicating a status of a received data packet; Output control means for temporarily increasing a transmission output for at least a portion of said second uplink control channel comprising said pilot information during a predetermined period during which said status signal is transmitted; Secondary station comprising a. The method of claim 6, A secondary station having an increase amount of the transmission output at the start of the predetermined period and a decrease amount of the transmission output at the end of the predetermined period. 8. The method according to claim 6 or 7, Means for increasing the transmission output by a different amount depending on whether the status signal is an acknowledgment or a negative acknowledgment. 8. The method according to claim 6 or 7, Means for increasing the transmission output by a first amount at the start of the predetermined period and increasing the transmission output by a second amount if the type of the state signal to be transmitted is determined, wherein the second amount is A secondary station that depends on whether the status signal is a positive or negative response. 8. The method according to claim 6 or 7, The communication system further comprises an uplink data channel, A gain factor is defined as the ratio between the transmit output of the second uplink control channel and the transmit output of the uplink data channel, The secondary station And means for adjusting the gain factor while the transmit power is increased to maintain the transmit power of the uplink data channel at a similar level as before the output increase. 8. The method according to claim 6 or 7, Means for resetting a timer upon detecting an indication that the data packet has been sent to the secondary station, The predetermined period of time lasts until the timer expires. Secondary station. 8. The method according to claim 6 or 7, Means for communicating with a plurality of primary stations simultaneously, receiving output control commands from each of the primary stations, and receiving the data packet from any one of the primary stations; Means for setting an uplink transmission output in accordance with an output control command received from the primary station that transmitted the packet during the duration of the predetermined period. As a method of driving a communication system, The communication system, A downlink data channel for transmitting data packets from the primary station to the secondary station, A first uplink control channel for transmitting information related to receiving the data packet from the secondary station to the primary station; Second uplink control channel for transmitting pilot information ≪ / RTI > The method, The secondary station receiving the data packet; The secondary station transmitting a status signal to the primary station via the first uplink control channel to indicate a status of a received data packet. Including, The secondary station temporarily increases the transmit power for at least a portion of the second uplink control channel containing the pilot information during a predetermined period during which the status signal is transmitted. How to drive a communication system.

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