Method for improving mobile radiocommunication system performances using a power control algorithm

The present invention generally relates to mobile wireless communication systems.

More specifically, the present invention relates to power control techniques used to improve performance (in terms of quality of service, capacity, etc.) in such systems.

The present invention is particularly applicable to CDMA ("code division multiple access") type mobile wireless communication systems. In particular, the present invention is applicable to UMTS (general purpose mobile remote communication system).

As is known, CDMA systems use two types of power control techniques: so-called open-loop power control techniques and so-called closed-loop power control techniques (also referred to as CLPC below). These power control techniques can be recalled with respect to the uplink transmission direction, i.e. the direction from MS (mobile station) to BTS (transceiver base station). In open-loop power control, the MS transmission power is controlled based on the power received from the BTS by this MS. In CLPC, MS transmission power is controlled based on the transmission quality estimated by this BTS of the link between this MS and BTS.

The transmission quality of the link between MS and BTS depends on the ratio of the received signal to the disturbing power, also known as the SIR (Signal to Interference Ratio). When the SIR of an MS is low, or equivalent, when the power of other MSs is much higher than that power, its performance drops dramatically. The CLPC algorithm allows each user's SIR to remain as close to the target SIR as possible.

The principle of the CLPC algorithm is to periodically estimate the SIR of the signal received from each MS and use BTS to target this estimated SIR (SIR)._target). If the estimated SIR is lower than the target SIR, the BTS sends a power control command to the MS to increase its transmitted power. Otherwise, the BTS sends a power control command to the MS so that the MS reduces the transmission power.

The target SIR is an important parameter in such a system. In fact, if the target SIR value is set higher than necessary, it will have unnecessary effects on the level of interference in the system, thus resulting in unnecessary degradation of system performance. On the other hand, if the target SIR value is set lower than necessary, the performance of running communication will deteriorate.

Generally, the target SIR is selected as a function of required quality of service and is currently tuned by the so-called external loop algorithm (as opposed to the previous one, also known as the internal loop algorithm). The principle of the external loop algorithm is to estimate the quality of service on a regular basis (generally represented by the bit error rate BER or frame error rate for voice services and the block error rate BLER for data packet services. This is to compare this estimated quality with the required service quality. If the estimated quality is lower than the required quality of service, the target SIR is increased. Otherwise, the target SIR will be reduced.

The outer loop algorithm needs to be slow, as opposed to the inner loop algorithm, which needs to be quick to track changes in SIR as accurately as possible. This is because quality needs to be averaged over a period of time in order to get reliable estimates. Usually, in a third generation system such as UMTS (general purpose mobile remote communication system), the SIR of the received signal is determined and compared to the target SIR at each slot in the frame, while The quality is averaged over several frames (a slot is a unit of data transmitted in such a system, that is, a basic time unit within a frame, and the frame duration is typically equal to 10 milliseconds, a slot. The duration is 1/15 of this frame duration).

However, such slow processing can cause serious problems, especially when so-called compression modes are used.

The downlink compression mode was introduced in UMTS to allow the user equipment (UE) to make measurements for the frequency difference from its downlink transmission frequency. The basis is to stop downlink transmission for a certain amount of time (or transmission gap). Simultaneous uplink and downlink compression modes can also be used when the measurement frequency is close to the uplink transmission frequency.

Since the instantaneous bit rate must be increased during the compressed frame (by increasing the coding rate and decreasing the spreading factor), the target SIR also needs to be increased by about the same rate.

In addition, closed-loop power control is no longer active during the downlink and uplink transmission gaps, resulting in significant performance degradation, primarily during compression and recovery frames (frames immediately following compression frames). To do. This degradation can reach several decibels. This effect also needs to be compensated by increasing the target SIR during these frames to maintain the same quality of service as in normal (ie uncompressed) mode.

However, the external loop power control algorithm is a slow process and will probably require several frames to change the target SIR accordingly. Therefore, this process seems too slow to be able to increase the target SIR at the required compression and recovery frames. In addition, the target SIR can even be increased immediately after the compression and recovery frames, where it is not needed.

<p> Therefore, compression mode requires faster processing than traditional external loop algorithms to avoid performance degradation.</p><p> More generally, any change in transmission requirements requires faster processing than traditional external algorithms, including the following: Change from uncompressed mode to compressed mode, or vice versa, change in transmission speed for required service changes (especially transmission speed changes), for any required service (eg data packet service) , Changes in environmental conditions (moving speed, radio propagation conditions, ...), etc.</p><p> Therefore, there is a general need for more efficient power control to improve performance.</p>

<p> Therefore, an object of the present invention is to use a power control algorithm for controlling transmission power according to a transmission quality target value and an adjustment algorithm for adjusting the transmission quality target value according to transmission requirements. A method for improving the performance of a mobile wireless communication system, wherein when a change in the transmission requirement occurs, the corresponding change is made to control the transmission quality target value in an expected manner. By applying it, it involves bypassing the tuning algorithm.</p><p> According to another object of the invention, the method further applies the corresponding changes in order to control the transmission power in an expected manner when the changes in the transmission requirements occur. It involves bypassing the power control algorithm.</p><p> This method further improves performance by allowing transmission power to approach new transmission quality targets as quickly as possible.</p><p> According to another object of the invention, said change in transmission requirements includes a change from uncompressed mode to compressed mode, said said corresponding change should be applied prior to the compressed frame, said transmission quality. Includes an increase in the target value.</p><p> According to another object of the present invention, said change in the transmission requirements includes a change from a non-compressed mode to a compressed mode, and said corresponding change includes compressed frame to be applied after a transmission gap of the arm, This includes an increase in the transmission quality target value.</p><p> According to another object of the invention, said change in transmission requirements includes a change from compressed mode to uncompressed mode, and said corresponding change should be applied after a compressed frame, said transmission quality goal. Includes value reduction.</p><p> According to another object of the invention, said change in transmission requirements includes a change from compressed mode to uncompressed mode, the corresponding change following a compressed frame ending in a transmission gap. Or it includes an increase in the transmission quality target value that should be applied between multiple recovery frames.</p><p> According to another object of the present invention, the transmission quality is represented by a signal-to-interference ratio.</p><p> According to another object of the present invention, the mobile wireless communication system is of the CDMA type.</p><p> According to another object of the present invention, the power control is performed in the uplink transmission direction of the mobile wireless communication system.</p><p> According to another object of the present invention, the power control is performed in the downlink transmission direction of the mobile radio communication system.</p><p> Another object of the present invention is a mobile radio communication system that includes at least a transmitting entity and a receiving entity for performing such a method, the first entity of said entity being the said transmission requirement. Means are provided to bypass the adjustment algorithm by applying the corresponding change to adjust the transmission quality target value in an expected manner when a change occurs.</p><p> According to another object of the invention, the first entity is provided with means for determining and / or updating the corresponding changes.</p><p> According to another object of the invention, the means for notifying the first entity of the previous value required to determine and / or update the corresponding change is a second entity of said entity. It is provided in the entity.</p><p> According to another object of the present invention, a means for notifying the first entity of the corresponding change is provided in the second entity of the entity.</p><p> According to another object of the present invention, a means for notifying the first entity of the occurrence of a change in the transmission requirement is provided in the second entity of the entity.</p><p> According to another object of the present invention, the second entity of the entity is provided with means for notifying the first entity of the corresponding change, as well as notifying the occurrence of a change in transmission requirements. ..</p><p> According to another object of the present invention, a means for recording the corresponding change is provided in any one of the two said entities.</p><p> According to another object of the present invention, one of the two said entities is a mobile radio communication network entity.</p><p> According to another object of the present invention, one of the two said entities is a mobile station.</p><p> Another object of the present invention is a mobile wireless communication network entity for performing such a method in the uplink transmission direction, which anticipates the transmission quality target value when the transmission requirements change. Includes means for bypassing the tuning algorithm by applying the corresponding changes to it so that it is tailored in the manner in which it is.</p><p> According to another object of the invention, the mobile radio communication network entity applies the corresponding changes to control the transmission power in an expected manner when the transmission requirements change occurs. This further includes means for bypassing the power control algorithm.</p><p> Another object of the present invention is a mobile station for performing such a method in the downlink transmission direction, in which the transmission quality target value is expected when the transmission requirement is changed. Includes means for bypassing the tuning algorithm by applying the corresponding changes to it, as is the tuning in.</p><p> According to another object of the present invention, the mobile station expects the transmission power when a change in the transmission requirements occurs in order to carry out such a method in the downlink transmission direction. Includes means for bypassing the power control algorithm by applying the corresponding changes to it, as controlled by.</p><p> Another object of the present invention is a mobile radio communication network entity for performing such a method in said downlink transmission direction, including means for notifying the mobile station of the corresponding change.</p><p> According to another object of the present invention, a mobile radio communication network entity provides a means for notifying a mobile station of the occurrence of a change in the transmission requirements in order to carry out such a method in the downlink transmission direction. Includes.</p><p> According to another object of the invention, a mobile radio communication network entity makes the corresponding change, along with a notification of the occurrence of a change in transmission requirements, in order to perform such a method in the downlink transmission direction. Includes means for notifying.</p><p> According to another object of the invention, said change in transmission requirements includes a change from uncompressed mode to compressed mode, and / or a change from compressed mode to uncompressed mode, and the notification is in compressed mode. Executed with parameter notification.</p><p> According to another object of the invention, said change in transmission requirements includes a change from uncompressed mode to compressed mode and / or a change from compressed mode to uncompressed mode, as described above. The changes to be made include components corresponding to the portion of the said change in transmission requirements due to the transmission gap of the compressed frame.</p><p> According to another object of the present invention, the notification is performed for each compressed frame.</p><p> According to another object of the present invention, if compressed frames occur periodically, the notification is executed only once for all compressed frames of such a defined period.</p><p> These and other objectives of the present invention will become more apparent in the description below, which will be considered in conjunction with the accompanying drawings.</p>

As recalled in FIG. 1, current power control processing includes an internal loop algorithm (also referred to herein as a power control algorithm) 1 and an external loop algorithm (also referred to herein as a tuning algorithm) 2. There is.

Internal loop algorithm 1 includes the following steps: In step 10, the receiving entity estimates the SIR received on average during period T, and in step 11, the receiving entity targets this SIR, SIR, SIR._targetCompare with SIR&gt; SIR_targetIf, in step 12, where δ is the power control step size of the algorithm, the receiving entity sends a "decrease" power control command to the transmitting entity and SIRs so that the transmitting entity reduces its power by δdB. &lt;SIR_targetIf, in step 13, the receiving entity sends an "increasing" power control command to the transmitter so that the transmitting entity increases its power by δdB.

This is repeated cyclically, as shown by loop 14.

External loop algorithm 2 includes the following steps. In step 15, the receiving entity estimates the average quality of reception (eg, BER) during the period T' T, and in step 16, the receiving entity targets this estimated BER BER (service request). Compared to (representing the quality to be done), BER&gt; BER_targetIf, then in step 17, SIR_targetIs reduced, BER &lt;BER_targetIf, then in step 18, SIR_targetIs increased.

This is repeated cyclically, as illustrated in Loop 19.

An example of a modification of the power control process to include the method according to the invention is disclosed below. However, it should be noted that this example is not limited and the present invention can be applied to algorithms of other examples.

In the example of Figure 2 (the same reference number as in Figure 1 points to the same element), a new step 20 is introduced. In this step 20, it is determined whether the transmission requirements have changed.

If no such changes have occurred, the external loop algorithm 2 is executed as in Figure 1.

If such changes have occurred, a new step 21 will be performed and the SIR will respond accordingly._targetThe corresponding changes are applied to adjust the value in the expected manner and thereby improve performance.

Also, in the example of FIG. 2, if such a change has not occurred, the internal loop algorithm is executed as in FIG. If such changes occur, a new step 22 is performed, and accordingly, the corresponding changes are applied to control the transmitted power in the expected manner, thereby further improving performance. To.

Corresponding to changes in transmission requirements, such corresponding changes can have predetermined values that can be determined in any manner.

For example, these can be considered system parameters and can be determined accordingly by the system operator. It is also desirable that these can be determined, especially by simulation. In either case, these can be updated during operation. These can also be determined in operation based on previously obtained values, for example by averaging. In any case, the predetermined value acquisition mode should take into account all factors that are likely to affect the corresponding change, or a combination of such factors.

Also, they are either of the two entities involved in the power control process (transmission entity and receive entity) that are used locally within this entity, or to the other of said entities for use by this entity. You can know that you will be notified.

They are also based on statistics on the values of either of the two said entities that are locally available within this entity or that were obtained prior to being notified to this entity by the other of the said entities. Can be determined and / or updated.

They can also be recorded in any of the entities and can be recovered when needed.

Also, the occurrence of a change in transmission requirements can be known locally by the entity responsible for applying the corresponding change, or this latter entity can be notified by another entity of said entity. ..

Therefore, all possibilities can be foreseen, and the examples given in this description should be understood only as illustrations and have no limiting nature.

FIG. 3 illustrates examples of means that can be used to perform the methods according to the invention for uplink power control within mobile radio communication network entities labeled 40 and within mobile stations labeled 41. It is a diagram intended for.

Mobile, especially within BTS (or node B within UMTS) representing "transceiver base station" and / or within BSC (or RNC within UMTS, representing "wireless network controller") representing "base station controller" The radio communication network entity 40 performs the transmission quality when a change in the transmission requirements occurs in order to perform the method in the uplink transmission direction (in addition to other traditional means not described herein). Means 42 for bypassing the adjustment algorithm by applying the corresponding changes to it so that the target value is adjusted in the expected manner may be included.

The mobile wireless communication network entity 40 performs the transmission in the uplink transmission direction (in addition to other traditional means not described herein) when a change in the transmission requirements occurs. It may also include means also labeled 42 for bypassing the power control algorithm by applying the corresponding changes to control the power in the expected manner.

Corresponding to such changes in transmission requirements, such corresponding changes can be determined, for example, by any of the aforementioned possibilities, eg, can have a predetermined value.

In any case, the mobile radio communication network entity 40 may include, for example, means 42'for recording the corresponding changes.

The mobile station 41 (or the user equipment UE in UMTS) causes a change in transmission requirements to perform the method in the uplink transmission direction (in addition to other traditional means not described here). It may include means 43 for notifying the mobile radio communication network entity.

FIG. 4 illustrates examples of means that can be used to perform the methods according to the invention for downlink power control within mobile radio communication network entities labeled 45 and within mobile stations labeled 46. It is a figure intended to be.

The mobile station 46 (or user equipment UE in UMTS) has undergone a change in the transmission requirements in order to perform the method in the downlink transmission direction (in addition to other traditional means not described herein). When this is done, means 48 for bypassing the adjustment algorithm by applying the corresponding changes to adjust the transmission quality target value in the expected manner may be included.

The mobile station 46 also uses the transmission power when changes in the transmission requirements occur in order to perform the method in the downlink transmission direction (in addition to other traditional means not described herein). It may also include means also labeled 48 for bypassing the power control algorithm by applying the corresponding changes to it so as to control in the expected manner.

Corresponding to such changes in transmission requirements, such corresponding changes can be determined, for example, by any of the aforementioned possibilities, eg, can have a predetermined value.

In certain embodiments, the mobile station 46 may include means 48 for recording the corresponding changes.

In another embodiment, the RNC for "wireless network controller" in BTS (or node B in UMTS), especially for "transceiver base station", and / or BSC (or in UMTS) for "base station controller". The mobile radio communication network entity 45, such as in), makes the corresponding modification to the mobile station 46 in order to perform the method in the downlink transmission direction (in addition to other traditional means not described herein). May include notification means 47 for transmitting.

The mobile radio communication network entity 45 may also include a means of notification, also labeled 47, for notifying the mobile station of the occurrence of a change in transmission requirements.

It is advantageous that the mobile radio communication network entity 45 may include notification means (also labeled 47) for notifying the mobile station 46 of the corresponding change, as well as notification of the occurrence of a change in transmission requirements.

The present invention can be applied in any case of a change in transmission requirements, for example any combination of any of the above cases, or any combination of such cases.

However, the present invention is of particular interest in combination with the use of compression modes, as described in detail below.

In order to keep the notification as low as possible, it is possible to separate the increase in target SIR due to the increase in instantaneous bit transmission rate from the increase in target SIR due to degraded performance at compressed frames, which can be described as follows: .. Δ_SIR= 10log (R_CF/ R) + δ_SIR

Where R is the instantaneous net bit transmission rate before and after the compressed frame, R_CFIs the instantaneous net bit transmission rate between compressed frames.

Bit transmission rate changes will be known by the UE, so an additional increase in target SIR due to degraded performance during compressed frames δ_SIRIt is possible to notify only. If this change is signaled with other compression mode parameters (including transmission gap length, periodicity, ...), the notification overhead can be low. For example, 2 bits have the following value δ_SIRAllows you to be notified. 00: 0dB 01: 0.5dB 10: 1dB 11: 2dB

Alternatively, Δ_SIRCan be notified directly, but requires a large number of bits.

The UE is immediately before the compressed frame (or immediately after the transmission gap of the compressed frame), Δ_SIROnly the target SIR would have to be increased and immediately after the compressed frame, it would have to be reduced again by the same value. This change in target SIR is made in addition to the normal downlink external loop algorithm that must be taken into account. At the same time, the UE can increase the transmission power by the same amount before the compression frame and decrease it immediately after the compression frame so that the downlink received SIR approaches this new target SIR as quickly as possible.

In addition, performance at the recovery frame may also be degraded due to interruptions in power control during the transmission gap, at least when the transmission gap is at the end of the compression frame. Therefore, it is also desirable to increase the target SIR in the recovery frame and notify the UE of this increase in the target SIR. Alternatively, the same value as for compressed frames (δ) to reduce the required notifications._SIR) Can be used.

Further, the notification can be executed for each compressed frame.

Alternatively, if the compressed frames occur periodically, the notification can be executed only once for all compressed frames of such a defined period in order to reduce the required notification. Is.

<figref num="1">It is a diagram intended to illustrate different steps of the current power control process (either uplink or downlink).</figref><figref num="2">FIG. 5 is intended to illustrate different steps of power control processing (either uplink or downlink) modified to include the method according to the invention.</figref><figref num="3">It is intended to illustrate examples of means that can be used within a mobile station and within a mobile radio communication network entity to perform the methods according to the invention with respect to uplink power control.</figref><figref num="4">It is intended to illustrate examples of means that can be used within a mobile station and within a mobile radio communication network entity to perform the methods according to the invention with respect to downlink power control.</figref>

Code description

1 Internal Loop Algorithm 2 External Loop Algorithm 40, 45 Mobile Radio Communication Network Entity 41, 46 Mobile Station 42, 47, 48 Means