System and method for high-speed dynamic link adaptation

The present invention relates to high speed dynamic link adaptation in mobile communication systems.

In 3rd generation (3G) communication systems, to compensate for degraded radio propagation conditions in which a user equipment (UE) must transmit with a transmission power greater than the maximum permissible or physical maximum transmission power. Dynamic Link Adaptation (DLA) is used for. Transmissions that require transmission at a power level greater than the maximum power level are transmitted at the maximum power level in 3G communication systems. When these signals are transmitted at maximum power level (these signals are less than their desired transmit power level), the performance of those signals may deteriorate, the error rate may increase, and the transmitted data may not be received. This will increase the nature and waste the system resources used.

One prior art method for dealing with this maximum power condition is to continue transmission with maximum permissible or physical maximum transmit power and rely on the error correction function of the receiver to correct any errors. That is. This ultimately results in undesired system performance. This is because the transmission will occur at a power level that is not sufficient to maintain the desired level of error rate performance.

Another way to accommodate maximum power conditions is to reduce the Uplink (UL) data requirement for periods when the transmit power required to maintain the desired level of error rate performance is greater than the maximum power capacity. That is. This method maintains the desired error rate performance by reducing the data rate.

By allowing an increase in the Block Error Rate (BLER), it is also possible to continue UL transmission when the desired power exceeds the maximum power capacity without affecting UL data requirements. This effect is considered unavoidable for the period from when the maximum power condition is perceived to when the UL transmission can be reset to an overall reduced rate. The 3G wireless standard specifies UE performance requirements that limit this period.

Transmissions that require a power level higher than the maximum transmit power level are likely to fail, so there is a strong motivation to exceed specified requirements. Services that allow data retransmission of failed transmissions increase overhead, reduce radio resource efficiency, and shorten UE battery life. For services that do not tolerate retransmissions, the increase in BLER will increase subsequent power demands to maintain the quality target of BLER. Since the UE is already transmitting at its maximum power, increasing the signal-to-interference ratio SIR target used in the UL transmit power control algorithm does not improve BLER performance for current channel conditions. If the channel conditions improve, the increased SIR target will reduce radio resource efficiency and battery life as the UE will have to transmit at higher power levels needed to maintain the desired performance.

Efficient ways to adjust UL transmission requirements are needed to meet or exceed performance requirements for improved quality of service (QoS).

In 3G communication systems, individual data streams are assigned to transport channels (TrCHs) with specific QoS capabilities, which are configured to meet specified BLER quality targets. The physical channel assigned to the UE supports multiple TrCHs at the same time. This is called a Coded Composite Transport Channel (CCTrCH). CCTrCH allows a variable amount of data to be present on each TrCH at any particular Transmission Time Interval (TTI). The TTI period is unique to each TrCH. Within each TTI period for a particular TrCH, the amount of data transmitted is defined by the Transport Format (TF).

For CCTrCH for any particular TTI period, the set of TFs for each TrCH is known as the Transport Format Combination (TFC). The set of all available TFCs (ie, all available allowable multiplexing options) is known as the Transport Format Combination Set (TFCS).

For each UL CCTrCH, the UE Medium Access Control (MAC) entity selects a TFC for transmission by TTI. This TFC and associated data is provided to the physical layer for transmission in the physical data request primitive. If the physical layer then determines that the transmission of this TFC exceeds the maximum or allowable UE transmission power, a physical status indicator primitive is generated for the MAC to signal that the maximum power or allowable transmission power has been reached.

When the MAC is notified that the maximum or allowable transmit power has been reached, the TFC that causes this condition to continue to exist is blocked unless the TFC cannot block according to the 3GPP standard. That is, it is removed from the set of available TFCs. Blocked TFCs are later restored to the set of available TFCs by unblocking them for a subsequent period of time when UE transmit power measurements indicate that they can support those TFCs below the maximum or allowed UE transmit power. Can be done.

<p> However, the current method of removing TFC has serious drawbacks. As mentioned above, the physical layer determines whether the TFC's transmission requires more than the maximum or allowed UE transmit power, and then puts a physical status indicator primitive to indicate that the maximum or allowed power has been reached. Generate for MAC entity. Using this method, the UE approximately reconfigures the set of available TFCs in order for the MAC to remove the blocked TFCs and start selecting TFCs from the updated set of available TFCs. It may be in maximum power for 60 milliseconds or more. The UE will reduce the TFC available only for TFC power requirements that exceed its transmit power capacity. The UE will then be more likely to opt for the TFC with the next lowest transmit power requirement. However, there is no guarantee that a reduced set of TFCs will not require more power than maximum power. This causes the process to be repeated once more to further reduce the set of TFCs, resulting in additional delays. For each TFC excluded, data and radio resources for a given TTI will be lost. After all, the performance of the system deteriorates during the period of maximum power conditions.</p><p> Further performance issues arise when the UE attempts to recover a TFC that was blocked due to maximum power conditions. It is desirable to unblock (ie recover) the TFC as quickly as possible to make the set of TFCs available for use by the UE more complete. After all, system performance will improve if TFC is restored efficiently.</p><p> Therefore, prior art methods of dealing with situations where the UE is in its maximum power state are far from satisfactory system performance. It would be desirable to have an improved way to quickly shrink the set of TFCs while reaching the maximum UE power condition and quickly restore the TFC when the maximum UE power condition is exhausted.</p>

<p> The present invention is a system and method for allowing efficient reduction of TFC within a TFCS to support the desired transmission while remaining within the power and data requirements. If the UE transmit power requirement exceeds the maximum or acceptable transmit power, reduce the set of TFCs to only acceptable TFCs that do not currently exceed the power limit. The UE will then choose from an acceptable reduction set of TFCs.</p><p> The present invention also supports pre-determination of unsupported TFCs. TFCs that require transmit power greater than the maximum or permissible UE transmit power are continuously determined for each TTI, not just TTIs that exceed the maximum power. The TFC selection process is adjusted to avoid selecting TFCs that exceed the transmit power capacity prior to transmission.</p><p> The present invention also allows the restoration of TFC in TFCS when the maximum power condition no longer exists.</p>

<figref num="1">It is a flow chart of efficient removal of TFC by this invention.</figref><figref num="2">It is a flow chart of the restoration of TFC in TFCS.</figref><figref num="3">It is a flow chart of the pre-removal of TFC by this invention.</figref><figref num="4">It is a flow chart of an alternative method corresponding to determining the TFC transmission power requirement on a regular basis.</figref><figref num="5">It is a flow chart of an alternative method corresponding to determining the TFC transmission power requirement on a regular basis.</figref><figref num="6">It is a block diagram of a MAC entity and a physical entity.</figref>

The present invention will be described with reference to the drawings. The same number represents the same element throughout.

The dynamic link adaptation according to the present invention has three basic aspects. First, if there are conditions where the UE transmit power requirement exceeds the UE's maximum or maximum allowable power, TFCs that require power that exceeds the maximum power limit are effectively blocked. All TFCs that currently exceed this limit will be notified to the MAC for subsequent TFC selections. After that, only TFCs that do not require more power than the UE transmit power limiting capability are available for selection.

Second, the present invention supports efficient recovery of TFC in TFCS when maximum power conditions no longer exist.

Finally, the present invention supports predetermination of unsupported TFCs, i.e. TFCs that require transmit power greater than the maximum or allowed UE transmission. These TFCs are determined continuously and regularly, not only for TTIs for which maximum power conditions exist, but also for each TTI. Each TTI may or may not include a TTI for which no data is transmitted. As TFC requirements change over time, this allows for pre-determination of TFCs that will not be supported.

It should be noted that although the present invention relates to the removal and restoration of TFC, the minimum set of TFC in the configured TFCS should always be available for transmission. Preferably, this minimum set is excluded from the TFC removal and restoration process described below.

The process of removing and restoring TFC is performed on a regular basis. The duration of these processes is described below as being based on one TTI, but it is also possible to perform actions approximately every TTI (ie, multiple times per TTI) or every few TTIs. .. Also note that each TTI may or may not include TTIs for which no data is transmitted.

With reference to FIG. 1, the procedure 10 for efficient removal of TFC according to the present invention is shown. Procedure 10 begins with selecting a TFC with a set of available TFCs (step 16). The set of TFCs available is the initial complete transport format combination set (TFCS) set up for the establishment of CCTrCH. The selected TFC is sent to physical entity 14 (step 18). The physical entity 14 determines the TFC transmit power requirement (step 22) and determines whether the UE transmit power required for this TFC exceeds the maximum or maximum allowed UE power (step 24). If not, steps 16, 18, 22 and 24 are repeated until the transmit power requirement for TFC exceeds the maximum permissible power. For TFC transmissions, if the UE power requirement exceeds the maximum allowed power, physical entity 14 determines all TFCs in the "overpowered state" within the TFCS (step 25). The physical entity 14 indicates the TFC's available or unavailable (ie blocked) status to the MAC entity 12 (step 26). Note that physical entity 14 can indicate the status of available TFCs, unavailable TFCs, or both. MAC entity 12 removes the overpowered TFC indicated by physical layer entity 14 from the set of available TFCs (step 28). Procedure 10 is then repeated for each TTI.

Although the function is specifically identified as being performed at the physical layer, some of these actions can also be performed at the MAC layer.

Refer to Figure 2 to show procedure 50 for restoring a TFC in an overpowered state. MAC entity 12 selects a TFC using the set of available TFCs (step 52). The set of available TFCs is the initial complete transport format combination set (TFCS) set when CCTrCH was established, or the set of available TFCs reduced from TFCS previously shown from physical entity 14. Is one of. The selected TFC is sent to physical entity 14 (step 53).

Physical entity 14 determines if any TFC is in an overpowered state (step 54). This determination is performed periodically only for TFCs that are in an overpowered state within the configured TFCS. This cycle may be, for example, every TTI. Physical entity 14 then determines if any of the TFCs that were in the overpowered state no longer exceed the maximum or maximum allowed power and can be restored to the set of available TFCs (step). 55). The physical entity 14 then shows the TFC to be restored to the MAC entity 12 (step 56). If there is a change in the available TFC (ie, if the TFC is unblocked), MAC entity 12 updates its list of available TFCs (step 58). Steps 52-58 are continuously repeated by the MAC and physical layer entities 12, 14. This procedure 50 ensures that when the TFC is blocked, the recovery of available TFC is continuously determined for each TTI, not just for TTIs that exceed maximum power.

Restoration of the TFC is much more efficient when the unblocked TFC is shown on a regular basis than as determined by the transmit power measurement calculated by the UE for the transmit signal. This is because the usual measurement reporting and processing mechanism is slow. This allows the UE to ensure that the transmit rate does not drop below the data rate supported by the current channel conditions. The UE can restore the desired TFC based on the expected transmit power requirements prior to transmission, reducing the time required to restore the TFC by one or more TTIs.

With reference to FIG. 3, the procedure 150 for pre-removal of TFC according to the present invention is shown. Procedure 150 initiates CCTrCh establishment and full TFCS setup (step 151). Then select a TFC from the set of available TFCs (step 152). MAC entity 12 sends the selected TFC to physical entity 14 (step 154). Physical entity 14 continually determines available TFCs on a regular basis, for example for each TTI, as shown in FIG. 3 (step 156). It is confirmed that all available TFCs can be sent. A determination is made as to whether any previously unblocked TFC is currently in the overpowered state (step 157). If not, procedure 150 returns to step 152 and repeats procedure 150. If so, the new TFC currently in overpowered state is shown to MAC entity 12 (step 158). MAC entity 12 updates the list of all available TFCs (step 160). Note that steps 152, 154 and 160 performed by MAC entity 12 and steps 156, 157 and 158 performed by physical entity 14 are repeated continuously, but do not necessarily have to be each TTI as shown in FIG. Please note that there is no such thing.

This method 150 allows for pre-determination of unsupported TFCs, as time-varying TFC transmit power requirements are checked on a regular basis, eg, for each TTI, restore. The TFC power requirement is checked at each TTI in step 156 to determine if it exceeds the maximum or maximum allowable power. If the power requirement cannot be met for a TFC that is not currently blocked, physical entity 14 indicates to MAC entity 12 that this TFC should be blocked (step 158). The TFC selection process is adjusted so that it does not select a TFC that exceeds its transmit power capacity prior to transmitting that TFC. In addition, if the power requirements for the currently blocked TFC can be met, the list of acceptable TFCs is continually updated so that previously blocked TFCs are restored.

The pre-determination may additionally use logic for determining a change in radio propagation conditions over time. For example, there are changes in path loss from the received reference channel and changes in reported uplink interference. Changes in these and other radio propagation conditions allow the UE to anticipate future transmit power requirements and block the TFC prior to interference, path loss, and other conditions that would cause the TFC to enter an overpowered state. ..

The pre-determination method 150 results in reduced UL data loss and efficient use of radio resources by proper TFC selection for successful transmission. By blocking the TFC before selecting and transmitting the TFC, the reduction in BLER improves the user's QoS and reduces the need for retransmissions to better utilize physical resources. Since the BLER of the TrCH is reduced, the corresponding unnecessary UL SIR target rise is avoided, and the reduction of UL transmission power further enhances the overall radio resource efficiency.

How to continuously update the available TFC 10, 50 and 150 improve performance, but the computational resources required to calculate the power requirements for each TFC and each TTI are significant. Therefore, referring to Figures 4 and 5, two alternative methods are shown to determine the TFC transmit power requirement, either periodically or by TTI.

Method 70 in Figure 4 begins with MAC entity 12 using the set of TFCs determined during the establishment or reconfiguration of CCTrCH (step 72). When CCTrCH is established or reconfigured, the TFCSs configured are sorted by TFC according to transmit power requirements (step 74). Note that although shown here at Physical Layer 14, the sorted TFC list may be determined by either Layer 2 or Layer 3 entities. In the TDD system, this list of TFCs may be timeslot-specific, such as a TFC list sorted by timeslot. Physical entity 14 periodically verifies its ability to transmit TFCs with the highest transmit power requirements (step 76). A determination is made as to whether the TFC can be transmitted (step 77). If this TFC can be sent, a determination is made as to whether any TFC was blocked (step 79). If so, make all previously blocked TFCs available (step 81), physical layer entity 14 should proceed to step 82, and all TFCs in the TFCS should be unblocked and are currently available. Show that there is in MAC entity 12. If not, procedure 70 returns to step 76.

On the other hand, if it is determined that the TFC with the highest transmit power requirement cannot be transmitted (step 77) or if the TFC with the highest transmit power requires a transmit power greater than the maximum allowable power, then in the sorted list. A procedure for estimating the status of each TFC is carried out (step 78). The specific process of efficiently determining which TFC should be blocked is not central to the present invention. This is because there are many alternative options available. For example, in the first alternative of the invention, there is a sorted TFC list, so check to determine if the middle TFC in the list can be sent. If you can't send it, check to see if you can send the TFC in the middle of the bottom half of the list. Similarly, if the TFC in the middle of the list can be sent, check to determine if the TFC in the middle of the top half of the list can be sent. This process is repeated until the TFC has the highest power requirement that can be transmitted. Another alternative is to apply a hash function to estimate the list index that exceeds its power capacity.

Physical entity 14 determines the unsupported TFC and the previously blocked and now supported TFC (step 80) and indicates the updated available TFC and the blocked TFC to the MAC entity (step 80). 82).

As an alternative to sending an updated complete list of unblocked TFCs, or a list of newly unblocked TFCs, from physical entity 14 to MAC entity 12, only an "index" to the sorted TFC list May be sent. For example, when the TFC list is sorted, entries above the index are blocked and entries below the index are unblocked. Sending the index will reduce the amount of control signaling required between physical entity 14 and MAC entity 12.

Physical measured or calculated values as a second alternative to sending an updated complete list of unblocked TFCs, or a list of newly unblocked TFCs, from physical entity 14 to MAC entity 12. It may be sent from entity 14 to MAC entity 12 (or another Layer 2 entity), which allows the Layer 2 entity to determine the new set of TFC available. Note that many of the steps shown in FIG. 4 as performed by physical entity 14 can also be performed by MAC entity 12, as in steps 78 and 80.

After that, steps 76 to 82 are repeated. When physical entity 14 sends an updated list of acceptable TFCs (or TFCS indexes or measured / calculated values) to MAC entity 12, MAC entity 12 updates the list of available TFCs (step 84).

Reference to Figure 5 shows a second alternative, 100, to determine TFC transmit power requirements on a regular basis. MAC entity 12 first uses the set of TFCs that were set when CCTrCH was established or reconfigured (step 102). Each TFC is associated with relative sensitivity when CCTrCH is established or reconfigured. This can be done by MAC entity 12, physical entity 14, or any Layer 2 or Layer 3 entity. This sensitivity should be mapped to integers 0-N with En / No requirements under certain propagation channel assumptions, maximum acceptable path loss under channel / transmit power assumptions, or otherwise. Can be done. In addition, in TDD systems, this relative sensitivity can also be time slot specific.

MAC entity 12 transfers the selected TFC to physical entity 14 (step 104). Physical entity 14 sends a TFC (step 106) and determines the margin for maximum power (step 108). The physical entity 14 uses its margins to identify which TFCs are blocked and which TFCs are unblocked (step 110). Note that this margin can be negative (which indicates potential blocking) or positive (which indicates potential recovery). These blocked and unblocked TFCs are then shown to MAC entity 12 (step 112). After that, the physical entity 14 repeats steps 106 to 112 at each TFC transmission. When MAC entity 12 receives instructions from physical entity 14 for blocked and unblocked TFCs, it updates the list of blocked and unblocked TFCs (step 114). Steps 104 and 114 are then repeated by MAC entity 12.

Referring to FIG. 6, a block diagram of MAC entity 12 and physical entity 14 is shown. MAC entity 12 includes a TFC selection processor 13 that selects TFCs for transmissions associated with a particular CCTrCH that supports the desired TrCH. Similarly, the physical entity 14 has a permissible TFC processor 15 that determines which TFCs are blocked and which TFCs are unblocked, and indicates which TFCs are blocked and which TFCs are unblocked to the TFC selection processor 13. Physical layer processing is preferred, but some of the above processing can also be performed within the MAC layer or other Layer 2 entities. According to the embodiments shown in FIGS. 4 and 5, the TFC processor 15 also sorts the TFCs by UE transmit power requirement. The sort list or relative sensitivity determination can also be determined by the TFC selection processor 13. Therefore, this process can also be performed on the physical layer, MAC or other Layer 2 entities, or Layer 3 entities. MAC entity 12 transfers the selected TFC 17 (selected from the available TFCs in the configured TFCS) to physical entity 14. In response, physical entity 14 indicates TFC blocking and unblocking (removal and restoration) 19.

Although methods 10, 50, and 150 are described above as separate procedures, these methods may be combined as desired for a particular application, as will be apparent to those skilled in the art. Often, it should be noted that the processes may be performed simultaneously. When combining the logic within methods 10, 50 and 150, some changes to the logic specified for each method are required to integrate these methods and achieve proper operation. Thus, although the invention has been described in connection with preferred embodiments, other modifications within the scope of the invention described in the claims will be apparent to those skilled in the art.