HK1124453B - Cognitive flow control based on channel quality conditions - Google Patents

Description

Cognitive flow control based on channel quality conditions

The invention is a divisional application of an invention patent application with the international application number of PCT/US03/14894, the international application date of 2003, 5/8/2003, the application number of 03810554.3 entering the Chinese national stage and the name of 'cognitive flow control based on channel quality conditions'.

Technical Field

The present invention relates to the field of radio communications, and more particularly, to the use of data transmission flow control between a Radio Network Controller (RNC) and a node B in a third generation (3G) communication system.

Background

A 3G Universal Terrestrial Radio Access Network (UTRAN) includes a number of RNCs, each RNC being associated with one or more node bs and each node B being further associated with one or more cells.

The 3G Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes generally use the RNC to distribute (i.e., buffer and schedule) data transmissions to at least one User Equipment (UE). However, for the high-speed channel of the 3G cellular system, data is scheduled for transmission by the node B. For example, one of these high speed channels is the high speed downlink shared channel (HS-DSCH). Since data is scheduled by the node B, data must be buffered at the node B for transmission to the ue(s).

Many examples of the large amount of data buffered at the node B that negatively impacts the overall operation of the system will be described later.

A first example is with respect to a retransmission mechanism in a 3G system to achieve a high confidence in end-to-end data transmission. Those skilled in the art will appreciate that transmission failure between the node B and the UE may be due to a number of different reasons. For example, the node B may have attempted to transmit several more times without success, or the transmission time for a particular transmission may have expired. The invention described in more detail below is intended to cover these situations and any other situation where a failure of a data transmission causes a retransmission by the Radio Link Controller (RLC).

There are many levels of retransmission mechanisms. Such as transmission by a hybrid automatic repeat request (H-ARQ) method, with a mechanism for High Speed Downlink Packet Access (HSDPA). The H-ARQ method provides a mechanism where erroneously received transmissions are indicated to the transmitter, and the transmitter retransmits the data until the data is correctly received.

In addition to the H-ARQ method, there are entities in the RNC and the UE. The transmitting RLC entity sends out a Sequence Number (SN) in the header of a particular communication Protocol Data Unit (PDU) that is used by the receiving RLC entity to ensure that no PDUs are missed during the transmission, and if there are PDUs missed during transmission (as known from out-of-sequence delivery of PDUs), the receiving RLC entity transmits a status report PDU that identifies the sequence number of the missed or received PDUs to inform the transmitting RLC entity that certain PDUs are missed. If the PDUs are delinked, the transmitting RLC entity retransmits a copy of the delinked PDU to the receiving RLC entity.

The impact of retransmission on system performance is described with reference to fig. 1. As shown, the RLC in the UE requires retransmission at its peer entity of the RNC when the PDU with SN-3 was not successfully received by the UE. At the same time, PDUs with SNs ═ 6 and 7 are queued in the buffer at the node B.

Referring to fig. 2, since the retransmission method requires some time and data continues to be transmitted, two more PDUs with SNs-8 and 9 have been arranged after PDUs with SNs-6 and 7 and before retransmitted PDUs with SN 3. The PDU with SN 3 must wait until PDUs with SNs-6-9 have been transmitted to the UE. In addition, due to the requirement of in-order delivery of data to higher layers, PDUs with SNs ═ 4-9 do not pass through higher layers until the PDU with SN ═ 3 is received and in-order delivery of data can proceed.

The UE is required to buffer the out-of-sequence data until an out-of-sequence PDU can be transmitted. This not only causes transmission delays, but also requires the UE to have sufficient memory to enable data buffering for continued data reception until the missed data can be successfully retransmitted. Otherwise, the effective data transmission speed is reduced, thereby affecting the quality of service. Since memory is very expensive, this is an undesirable design constraint. Thus, the first example is when RLC retransmissions are required and the large amount of data buffered at the node B results in large data transmission delays and high UE memory requirements.

A second example is when the buffering of data at the node B negatively impacts system performance as layer 2(L2) or layer 3(L3) signaling and data transmission are performed by the same scheduling method or share a single buffer at the node B. Although the data is buffered and proceeding with the L2/3 signal behind it, the signal cannot bypass the transmit arrangement. The larger the amount of data in the transmit buffer (which operates as a first-in-first-out (FIFO) buffer), the longer the L2/3 signal or data will take to pass through the buffer. Any high priority L2/3 signal is delayed by data in the buffer.

A third example is when buffering of data at the node B negatively impacts system performance due to a serving HS-DSCH cell change. Since the node-B performs scheduling and buffering of HS-DSCH data, when the UE performs a serving HS-DSCH cell change from a source node-B to a target node-B, there is a mechanism that may be a significant amount of data that remains buffered at the source node-B after handover, which is unrecoverable because there is no data buffering within the UTRAN structure when the source node-B is about to be transmitted to the target node-B. When the serving HS-DSCH cell changes, the RNC does not have any information about how much data (if any) is missing, since the RNC does not know what kind of data is buffered at the source node B. In the case of an HS-DSCH cell change, the greater the amount of data buffered at the node B, the greater the amount of data that will eventually be retained at the source node B and must be retransmitted.

It is therefore desirable to limit the amount of data buffered at the node B for the reasons discussed above.

Disclosure of Invention

The present invention is a system and method for improving the performance of a wireless communication system by intelligently using the control of data flow between the RNC and the node B. The system monitors certain criteria and appropriately increases or decreases the flow of data between the RNC and the node B if necessary. This improves the performance of the transmission system by allowing retransmitted data, signaling steps, and other data to be successfully received at a faster rate than in prior art systems by reducing the amount of data buffered at the node B. When channel quality degrades, data flow control is employed to reduce buffering at the node B and prior to HS-DSCH handover.

In a preferred embodiment, the present invention is implemented in a wireless communication system including a Radio Network Controller (RNC) in communication with a node B having at least one buffer therebetween for storing data. The RNC signals the node B and requests the RNC to send a certain amount of data to the node B. The node B monitors the selected quality indicators and calculates a size distribution of a buffer based on the selected quality indicators. The node B signals capacity distribution to the RNC. In response to receiving the capacity distribution, the RNC transmits data to the node B at a data flow rate determined in accordance with the capacity distribution.

Drawings

A more detailed understanding of the present invention can be derived from the following description, examples, and related drawings, in which:

figure 1 shows prior art buffering of data at the RNC, the node B, and the UE.

Figure 2 shows prior art buffering of data at the RNC, the node B, and the UE in case of retransmission.

Fig. 3A and 3B together monitor channel quality and regulate data flow between the RNC and the node B in accordance with the method of the present invention.

Fig. 4 is a diagram of buffering of data at the RNC, the node B, and the UE in case of retransmission, using the method of fig. 3A and 3B.

Detailed Description

The present invention is described with reference to the drawings, wherein like numerals represent like elements. Although the present invention is described with reference to a particular number of PDUs arranged in a buffer (e.g., ten PDUs), the number of PDUs mentioned herein is for simplicity purposes only, and the actual number of PDUs transmitted and buffered according to the previous example is more likely to be hundreds of PDUs or more. The present invention and its intent are intended to be applicable to any number of PDUs and any size transmission buffer.

In general, the present invention reduces data flow to the node B for a UE when the UE's channel quality degrades, and increases data flow to the node B when the UE's channel quality improves. To control the flow of data between the RNC and the node B, the present invention monitors one or more parameters of channel quality, which may be based on one criterion or a combination of a number of different criteria. In addition, as described in more detail below, the criteria can be generated internally by the node B or can be generated by an external entity (e.g., the UE) and transmitted to the node B.

Referring to fig. 3A, a method 50 of monitoring communication channel quality and adjusting data flow between the RNC52 and the node B54 in accordance with the present invention is shown. The method 50 handles data transmission between the RNC52 and the node B54. the RNC52 sends a capacity request to the node B54 (step 58). Basically the capacity request is a request from the RNC52 to the node B54 causing the RNC52 to send an amount of data to the node B54, the node B54 receives the capacity request and monitors the selected quality indicators (step 60). The selected quality indicator may be based on data transmitted from the UE (as described in more detail below) or may be based on an internally generated quality indicator, such as the depth of the buffer at the node B54.

The node B54 also monitors the status of buffers within the node B (step 62). As will be appreciated by those skilled in the art, although the present invention is described for simplicity with reference to a single buffer within the node B54, most of the buffer includes a plurality of buffers or a single buffer divided into a plurality of sub-buffers, each buffer or sub-buffer being allocated one or more data streams. An indicator is generated internally in the node B that indicates the amount of data in the buffer, whether or not there are one or more multiple buffers. This allows the node B54 to monitor the amount of data in the buffer and also monitor the amount of additional data that is acceptable to the buffer.

The node B54 calculates and sends (step 64) a capacity distribution to the RNC52, the capacity distribution being authorized by the node B54 to allow the RNC52 to send out a certain amount of data. Upon receiving the capacity distribution, the RNC52 transmits data according to the distribution (step 66), i.e., the RNC52 transmits data to the node bs 54 in an amount that does not exceed the capacity distribution. The node B then adjusts its buffer accordingly to accommodate and store the data (step 69). The amount of data stored in the buffer varies depending on the incoming data transmitted by the RNC52 and the outgoing data transmitted to the UE82 (shown in fig. 3B).

Those skilled in the art will appreciate that the method 50 shown in fig. 3A may be repeated constantly as data flows from the RNC52 to the node B54 and as the flow rate continues to be adjusted by the node B54. It should also be noted that method steps 58, 60, 62, 64, 66, and 69 need not be performed sequentially, and any one step may be performed multiple times before different steps of method 50 are performed. In addition, some steps, such as capacity distribution step 64, may display a repeating data distribution such that data transmission (step 66) may be performed periodically.

Referring to fig. 3B, a method 80 of monitoring the quality of the communication channel between the node B54 and the UE82 in accordance with the present invention is shown. The node B54 transmits data to the UE82 (step 84). The UE82 receives the data and transmits a signal quality indicator (step 86), such as a Channel Quality Index (CQI), to the node B54. This signal quality indicator is then used as the selected quality indicator in step 60 of fig. 3A.

It should be noted by those skilled in the art that method steps 84 and 86 need not be performed sequentially, e.g., in FDD mode, whether data is transmitted or not, signal quality indicators are periodically transmitted from the UE82, in which case the UE82 may periodically or in response to certain events transmit a signal quality indicator to the node B54, which is then used as the selected quality indicator in step 60 of fig. 3A.

As described above, the selected quality indicator may be generated internally by the node B or generated externally by another entity (e.g., the UE) and sent to the node B. According to a first embodiment, the criterion is channel quality feedback from the UE. In this embodiment, a CQI, which is an indicator of the downlink channel quality, is used.

In a second embodiment, the criterion is the ACK or NACK that the UE generates according to the H-ARQ method. For example, the number of ACKs and/or NACKs may be used to obtain an indication of channel quality over a period of time.

In a third embodiment, the criteria is the Modulation and Coding Set (MCS) selected by the node B that is needed to successfully transmit data. As can be appreciated by those skilled in the art, a very strong MCS is used when the channel conditions are poor. Alternatively, when the channel conditions are good, a less aggressive MCS is used and a large amount of data is transmitted. The selection of the strongest MCS set may be used as a pointer to poor channel quality conditions, but the use of the least aggressive MCS may indicate that channel quality conditions are good.

In a fourth embodiment, the criterion is the depth of a line within the node B transmission buffer. For example, if the node-B54 buffer is currently storing a large amount of data, the indicator of channel quality conditions may be poor since the data is "moved backward" in the node-B transmit buffer. A slightly loaded buffer may have channel quality conditions that are good indicators and the data has not moved backwards.

In a fifth embodiment, the criterion is the amount of data "dropped" at the node B. As is known by those skilled in the art, dropped data is data that the node B attempts to retransmit data several times and has been dropped after a predetermined number of attempts, which is an indicator that channel quality conditions are poor if a large number of transmissions are dropped by the node B.

In a sixth embodiment, the criterion is the amount of data that can be transmitted by the node B within a predetermined time (e.g., one hundred milliseconds). Depending on the quality of the communication channel, the number of PDUs buffered at the node-B may vary. Although the predetermined time may be fixed, the amount of PDUs that may be transmitted within the predetermined time may be significantly changed due to changing channel quality conditions. For example, if channel quality conditions are good, one hundred PDUs may be transmitted in one hundred milliseconds; however, if the channel quality conditions are very poor, only ten PDUs may be transmitted in a hundred seconds.

Those skilled in the art will appreciate that other criteria that may directly or indirectly indicate channel conditions may be utilized in accordance with the present invention. In addition, combinations of two or more of the above criteria may be utilized or weighted accordingly, depending on the particular needs of the system user.

Referring to fig. 4, the benefit of properly controlling the flow of data between the RNC and the node B can be seen. This example is an example where retransmission is required due to failed transmissions and the data flow between the RNC and the node B is reduced. The result of the data flow reduction is that only one additional PDU with SN-8 is arranged before the retransmitted PDU with SN-3. As shown in fig. 4, the use of data flow control reduces the delay of retransmission of PDUs with SN-3 compared to the prior art process shown in fig. 2 (PDUs with SNs-8 and arranged before PDUs with SN-3), so that PDUs with SN-3 can be retransmitted to the UE early. The ordered transfer requires faster processing and transfers of PDUs 4-8 to higher layers.

While the invention has been described in terms of preferred embodiments, other variations which are within the scope of the invention as set forth in the claims will be apparent to those skilled in the art.

Claims (13)

1. A method for a radio network controller, the method comprising:

sending a capacity requirement to a node B, wherein the capacity requirement indicates a certain amount of data of a high-speed downlink shared channel;

receiving a capacity profile from the node B in response to the capacity requirement, the capacity profile being based on one or more monitored channel quality parameters and indicating a number of protocol data units of a data flow associated with the high speed downlink shared channel that the radio network controller is allowed to transmit; and

transmitting a protocol data unit to the node B according to the capacity distribution.

2. The method of claim 1, wherein the capacity distribution is a grant by the node B to allow the radio network controller to transmit an amount of protocol data units.

3. A radio network controller, the radio network controller comprising:

circuitry configured to communicate a capacity requirement to a node B, the capacity requirement indicating an amount of data for a high speed downlink shared channel;

circuitry configured to receive a capacity profile from the node B in response to the capacity requirement, the capacity profile based on one or more monitored channel quality parameters and the capacity profile indicating a number of protocol data units of a data flow associated with the high speed downlink shared channel that the radio network controller is allowed to transmit; and

circuitry configured to transmit protocol data units to the node B according to the capacity distribution.

4. The radio network controller of claim 3, wherein the capacity distribution is a grant by the node B that allows the radio network controller to transmit an amount of protocol data units.

5. A method for a node B, the method comprising:

receiving a capacity requirement from a radio network controller, the capacity requirement indicating an amount of data for a high speed downlink shared channel;

transmitting a capacity profile to the radio network controller in response to the capacity requirement, the capacity profile being based on one or more monitored channel quality parameters and the capacity profile indicating a number of protocol data units of a data flow associated with the high speed downlink shared channel that the radio network controller is allowed to transmit; and

receiving a protocol data unit from the radio network controller according to the capacity distribution.

6. The method of claim 5, wherein the capacity distribution is a grant by the node B to allow the radio network controller to transmit an amount of data.

7. The method of claim 5, further comprising transmitting the received protocol data unit to a user equipment over the high speed downlink shared channel.

8. The method according to any of claims 5, 6 or 7, further comprising storing protocol data units received from the radio network controller in a node B buffer.

9. A node B, comprising:

means configured to receive a capacity requirement from a radio network controller, the capacity requirement indicating an amount of data for a high speed downlink shared channel;

means configured to transmit a capacity profile to the radio network controller in response to the capacity requirement, the capacity profile being based on one or more monitored channel quality parameters and the capacity profile indicating a number of protocol data units of a data flow associated with the high speed downlink shared channel that the radio network controller is allowed to transmit; and

means configured to receive protocol data units from the radio network controller according to the capacity distribution.

10. The node B of claim 9, wherein the capacity distribution is a grant by the node B to allow the radio network controller to transmit an amount of data, the node B further comprising:

means configured to transmit the received protocol data unit to a user equipment over the high speed downlink shared channel.

11. The node B according to any of claims 9 or 10, further comprising:

means configured to store protocol data units received from the radio network controller.

12. A method for a wireless transmit/receive unit, the method comprising:

receiving a high-speed downlink shared channel carrying a protocol data unit from a node B; and

sending quality information to the node B to facilitate the node B to send a capacity profile to a radio network controller, the capacity profile indicating a number of protocol data units of a data flow associated with the high speed downlink shared channel that the radio network controller is allowed to send.

13. The method of claim 12, wherein the capacity distribution is a grant by the node B to allow the radio network controller to transmit an amount of protocol data units.