CN1759544A

CN1759544A - Definite method of reference power in download power balancing technology under case of soft handover

Info

Publication number: CN1759544A
Application number: CNA038262010A
Authority: CN
Inventors: 刘晟; 赵柏峻
Original assignee: UTStarcom China Co Ltd
Current assignee: UTStarcom China Co Ltd
Priority date: 2003-03-28
Filing date: 2003-03-28
Publication date: 2006-04-12
Anticipated expiration: 2023-03-28
Also published as: CN100372258C; WO2004086650A1; AU2003221237A1

Abstract

The invention discloses the method for down link reference power in a kind of definite case of soft handover, comprise the steps: first step, wherein radio network controller (RNC) obtains transmitter code power and obtains for reflecting the measurement parameter of relative path loss size from participating in a plurality of Node B of a user equipment (UE) soft handover; And second step, under the condition that the result that wherein RNC utilization obtains remains unchanged at the current total received power of this UE, determine the down link reference power that i Node B distributed to UE .The invention also discloses the corresponding device of determining down link reference power in case of soft handover.

Description

Definite method of reference power in download power balancing technology under case of soft handover

In the downlink power balancing technique under the condition of soft switching

Method for determining reference power and its device

The present invention relates to Code Division Multiple Access (CDMA) communication systems, and more particularly, to a method and system for determining reference power in downlink power balancing technology in a CDMA system under soft handoff. Background

In a CDMA communication system, the capacity and coverage performance of the system is highly dependent on the interference experienced by the users. Among them, the power control technique has become a key technique of the CDMA communication system as an effective means for reducing the inter-channel interference. In practical CDMA systems, closed loop power control is the primary means of power control, and typically consists of an inner and an outer loop.

Fig. 1 shows a diagram of downlink inner loop power control in the prior art. The inner loop power control receiving end obtains an estimated value of signal-to-interference ratio (SIR) by measuring a received signal, compares the estimated value with an SIR target value obtained by outer loop power control to generate a power control command for transmitting power of the transmitting end, transmits the command to the transmitting end through a reverse channel, and increases or decreases the current transmitting power according to the command and a certain adjustment step length. Thus, inner loop power control is a feedback type power control technique. The outer loop power control is responsible for generating the required target SIR for the inner loop power control by adjusting the SIR target value to track changes in the radio channel environment to maintain the quality of service (QoS) agreed by the system at service set-up.

Inner loop power control is applicable to both the uplink and downlink. Hereinafter, an inner loop power control procedure of a downlink will be described by taking a Wideband Code Division Multiple Access (WCDMA) system of the third generation partnership project (3 GPP) as an example.

In WCDMA systems, downlink closed loop power control is mainly applied to the downlink Dedicated Physical Channel (DPCH). In the uplink Dedicated Physical Control Channel (DPCCH), there is a Transmit Power Control (TPC) field that conveys power control commands generated by the mobile station (i.e., user equipment UE) to the downlink DPCH channel transmitted by the base station (i.e., node B). TPC =1 if node B is required to increase downlink transmit power, and t o0 if node B is required to decrease downlink transmit power.

In a particular implementation, the execution of downlink inner loop power control commands is typically done by nodes beta. According to the 3GPP protocol TS25.214, first, the node b receives the uplink DPCCH channel from the UE and estimates the TPC command. Then, the current transmit power P (k-l) is updated according to the following formula:

P(k)= P(k-l) +P_TPC(k) +P_baeach parameter in the formula (k) (1) is expressed in decibels (dB), P_TPC(k) For the inner loop power adjustment generated based on TPC commands, if ^ C! The power control step size of the inner loop is defined as P, when there is no power increase limitation_TPC(k) Calculated as follows:

1

0

pbai (k) in equation (1) is a correction amount to prevent downlink power drift in soft handover. To clarify the cause of the correction amount, the macro diversity technique in soft handover in the CDMA system and the downlink power drift problem in the case of soft handover will be described below.

An important technical feature unique to CDMA systems is the support of soft handover, i.e. the mobile station does not immediately interrupt the radio link with the original node B when it starts to establish a new radio link with a target node B during handover, i.e. the mobile station is able to maintain communication with two or more node bs simultaneously. Fig. 2 shows a schematic diagram of a soft handover of a WCDMA system, where node bs are controlled by a Radio Network Controller (RNC) and a UE communicates with two node bs simultaneously. Here, only two node bs are depicted for convenience of illustration, but in practice there may be more.

The reception of uplink and downlink signals in soft handoff can utilize macro diversity techniques specific to soft handoff, and the resulting soft handoff gain can improve the coverage and throughput performance of a CDMA network. As shown in fig. 2, in the downlink direction, the UE may perform maximum ratio combining on downlink signals from different node bs. In the uplink direction, each node B processes the same uplink signal from the UE, and the decoded data frames are finally sent to the RNC for further combining.

Although the uplink data frames can be macro-diversity combined in the RNC, the TPC fields of the uplink DPCCH are individually detected by the node bs and applied to the respective inner-loop power control units, and cannot be combined by the RNC. Otherwise, the inner loop power control will generate a large delay, and the control rate and tracking performance of the inner loop power control will be greatly reduced. Thus, the reception of downlink power control commands does not have the soft handoff gain created by macro diversity. Thus, although there is only one downlink power control command generated by the UE, since the signals arriving at different base stations on the uplink DPCCH channel carrying the command undergo different paths, they have different SIRs, and since no soft handover gain is available, the reliability of the power control bits TPC is less than that of the data bits. Therefore, each node B may have a certain error in decoding the downlink power control command, and the error may occur differently. One possible scenario is: one base station reduces the transmit power to a UE while another base station increases the transmit power to the UE. That is, during soft handover, downlink power drift occurs in the downlink due to erroneous decoding of downlink power control commands by different base stations.

Downlink power drift is unacceptable because it greatly reduces the performance of downlink soft handoff. To compensate for the effect of power drift, it is common practice to add a power balance adjustment loop to the inner loop power control, which is also used in WCDMA, and the correction P in equation (1)_bal(k) It is based on this technology introduction. In the 3GPP Standard TS25.433 and in the document TSGR1-01-0197, P is given_bal(k) The conditions to be satisfied are: sigma P_bal(k) = (l - ) (3)k

The sum on the left in equation (3) represents the total power balance adjustment, P, over an adjustment period_refIs the downlink reference power, P_initIs the initial value of the downlink power at the beginning of the adjustment period, and r is a convergence factor between 0 and 1, which is used to control the proportion of the total power adjustment in each adjustment period. Parameter adjustment period, P, in equation (3)_refAnd r is transmitted by the RNC to the node B via a signalling path NBAP (node B application part) between the RNC and the node B. Where the adjustment period and r are generally relatively fixed parameters taken empirically, and P is_refIs calculated by the RNC based on the dedicated measurement results of the node B. And P_refThe specific measurements for calculating the relevant node B mainly include SIR and transmitted code power, and the specific measurements for the node B can refer to protocols such as TS25.433, TS25.215 and TS25.133 of 3 GPP.

Patent application WO02/25836 "downlink power control in cellular telecommunications network" teaches a node B determining the correction P for the power balance adjustment loop using the parameters provided by the RNC, provided that equation (3) is satisfied_bal(k) The method of (1). Meanwhile, the patent application WO01/71941 "determination of reference power level in diversity handover base station" gives the downlink reference power P_refThe method of (3). The downlink reference power P proposed in patent application WO01/71941, among others_refThe calculation method of (2) is summarized as taking the downlink reference power as the average of the sum of the average transmitted code powers of the base stations, or the average transmitted code power of the leading base station (the base station with the largest uplink received signal SIR).

The following problems exist with the aforementioned downlink reference power calculation method: the result of the downlink power balance adjustment loop is to make the average value of the downlink power of each base station tend to the downlink reference power, thereby changing the distribution proportion of the current base station transmitting power. Thus, even if the total transmission power of each base station is controlled by the inner-loop power before the power balance adjustment to satisfy the reception SIR requirement of the mobile station, the total transmission power after the adjustment will hardly satisfy the reception SIR requirement of the mobile station because the calculation of the downlink reference power in the prior art does not take into account the difference in the downlink path loss of each base station to the mobile station. That is, the unreasonable downlink reference power may cause the power balance adjustment loop to adversely affect the inner loop power control, thereby degrading the tracking performance of the downlink inner loop power control.

On the other hand, patent applications WO01/47145 and US6104933, etc. relate to methods for allocating downlink transmit power in soft handover situations. They all propose that in the case of soft handover, the allocation scheme for optimizing the downlink transmission power of each base station should be inversely proportional to the downlink path loss, i.e. under the condition of ensuring the same mobile station receiving rate, the base station with larger downlink path loss should allocate less power, and the base station with smaller downlink path loss should allocate more power. Therefore, the total downlink transmitting power can be minimized, thereby reducing the interference to other channels and being beneficial to increasing the channel capacity.

As can be seen from the above-mentioned downlink transmission power optimization allocation scheme, the prior art is disadvantageous in that the same downlink reference power is used in determining the allocation, and as a result, each base station tends to transmit the same power. Disclosure of Invention

In order to overcome the above problems, the present invention provides a method for determining a reference power in a downlink power balancing technique under an effective soft handover condition.

The method for determining the downlink reference power in the soft handover condition comprises the following steps: a first step in which a radio network controller RNC obtains transmission code power from a plurality of node Bs involved in soft handover of a user equipment UE and obtains measurement parameters reflecting the magnitude of relative path loss; and a second step in which the RNC determines the downlink reference power P allocated to the UE by the i-th node B using the obtained result on the condition that the current total received power of the UE remains unchanged.

The method of the invention considers the current total receiving power value of the UE to be switched, determines the downlink reference power under the premise of keeping the value unchanged, thereby not influencing the downlink reference power

The inner loop power control of the UE itself is balanced.

According to a preferred embodiment of the present invention, the downlink reference power ref m allocated to the UE by the ith node B is determined by the following equation in consideration of the optimized downlink reference power allocation scheme

∑^Lj^aj

Wherein m represents the number of node Bs participating in soft handover, and represents the average downlink loss from the jth node to the UE. A parameter (representing the downlink power ratio of the ith node B allocated by the RNC relative to the 1 st node B) is introduced here to enable each node B to allocate downlink reference power in different proportions. When the values of all the node Bs participating in the soft handover are 1, the adopted mode is still the traditional equal-power distribution mode. If the values of different node Bs are different, an optimized downlink reference power allocation scheme can be realized.

According to another preferred mode of the invention, the downlink reference power V 'allocated to the UE by the ith node is determined by'_ref

Where the SIR of any one node B is indicated. The reason why it is preferable to use the measurement values of the node B instead of the measurement values of the UE | is that the measurement report of the node B does not occupy radio channel resources compared to the measurement inclusion of the UE, and the problem that it is difficult to keep the UE and the node B measurement values consistent in time is avoided.

The present invention also provides an apparatus for determining a downlink reference power in a soft handover situation, comprising: an obtaining means for obtaining a first step of transmitting code power from a plurality of node bs participating in a soft handover of a user equipment UE and obtaining a measurement parameter reflecting a relative path loss magnitude; and determining means for determining the downlink reference power P allocated to the UE by the ^ i node Bs under the condition that the current total received power of the UE remains unchanged according to the result obtained by the obtaining means. Drawings

The above and other advantages of the present invention will become more apparent by describing in detail preferred embodiments of the present invention with reference to the attached drawings. In the drawings:

FIG. 1 is a diagram illustrating downlink inner loop power control in the prior art;

FIG. 2 is a schematic diagram of a soft handover procedure;

FIG. 3 is a block diagram of a method according to the present invention;

FIG. 4 is a block diagram of a system according to the present invention;

fig. 5 is a detailed representation of the method shown in fig. 3. Detailed Description

Fig. 3 is a block diagram of a method according to the invention. As mentioned previously, the downlink reference power P_refIs determined by the RNC based on node B specific measurements. In step 302, the RNC may request each node B involved in the soft handover to report the respective transmit code power. At the same time, the RNC may control the node B to perform a predetermined smoothing filtering process before the measurement report, or may perform further averaging and other processes on the measurement report result in the RNC, so that the obtained power value may be used as an estimated value of the current downlink transmission code power of the node B.

In addition, the RNC also needs to obtain measurement parameters reflecting the relative magnitude of the downlink path loss. It will be appreciated by those skilled in the art that these measured parameters may be varied and obtained in a variety of ways, for example, by direct measurement or by conversion with other values. The measurement parameter may include (but is not limited to) UE measured received Signal code Power/WCP of common Pilot channel CPICH_OTCW,,，

The downlink path loss measured by the UE, or the received signal SIR measured by each of the node bs.

Next, in step 304, the RNC determines the downlink reference power allocated by each node B for subsequent power balance adjustment if the current total received power of the UE remains unchanged.

Fig. 4 illustrates in detail a block diagram of an arrangement according to the invention. The RNC includes an acquiring means for acquiring the transmission code power reported by each node B and acquiring the aforementioned measurement parameter reflecting the relative magnitude of the downlink path loss, and a determining means for determining the downlink reference power allocated to the UE by each node B for the subsequent power balance adjustment loop, in the case that the current total received power of the UE remains unchanged. It should be understood that the lines shown in fig. 4 represent logical connections only.

Hereinafter, the principle of the method according to the present invention will be described in detail.

First, for the convenience of analysis, all the power-related parameters below are represented linearly. It will be appreciated by those skilled in the art that the present invention is not limited to linear representations and is equally applicable where other representations are used, such as logarithmic.

If m node Bs are in soft handover connection with the UE, and the estimation value of the current downlink transmission code power of each node B can be expressed as the average path loss of the downlink from each node B to the UE is Li, the total power P currently received by the UE is:'

,= .ΡΓ (4) j=l

As mentioned above, the result of the downlink power balance adjustment loop is to make the average value of the downlink power of each node B trend to the downlink reference power, so the downlink power of each node B when the downlink power balance adjustment loop converges, i.e. the downlink reference transmit power P of each node B set by the RNC, should satisfy the following equation:

= ai - 2,3, ...... m , a. = 1 (5 ） rref

it can be seen that equation (5 a) indicates that the total power received by the UE should remain unchanged after the downlink power balance adjustment, so that the downlink power balance adjustment loop does not affect the inner loop power control, in equation (5B), α, the downlink reference power of the ith node B allocated to the RNC is relative to the downlink reference power of a first node B.

∑^LJ J if reference is made to the downlink transmission power scheme of each node B in case of soft handover as proposed in patent application WO01/47145 and patent US6104933, etc., it is advisable:

a (7) at this time, the downlink reference transmission power of each node B is:

j=\

if the normal equal power allocation is adopted, that is, =1, i = \ X.. m, the downlink reference transmission power of each node B is:

here, the average path loss of the downlink from the ith node B to the UE is unknown, and can be obtained by the following two methods. One method is to count by the following formula

L—— RS( P_CPICHJ (10)

, CPICH^

In the formula, RSCP is the downlink transmission power of CPICH of each node BETA common pilot channel_OTOTThe corresponding CPICH received signal code power measured for the UE. The calculation of this equation can be done by the UE, which obtains the known P from the cell broadcast_C ^T _P ^X _{1CH J}It can also be calculated by the RNC, when the UE directly reports the measured value of RSCP o/, which is a known quantity of the RNC.

On the other hand, different node bs receive the same uplink signal from the UE in the uplink direction. Therefore, the ratio of the uplink average path loss is the ratio of the uplink received code power of each node B. Although the uplink received code power is not the node B measurement specified in the standard, the ratio of the uplink average pathloss can be approximated by the ratio of the uplink received signal SIR if the difference in uplink interference magnitude between the node bs is ignored. Meanwhile, in the frequency division duplex WCDMA system, the uplink and downlink wireless links have approximately equal average path loss because the carrier frequencies are closer and experience the same spatial propagation path. Thus, the ratio of the downlink average path loss can be expressed as:

(11)

l) SIR, and using the result, the downlink reference transmission power of each node B shown in equation (6) is:

the measured SIR using the node B is better than the measured RSCP using the UE because the measurement report of the node B does not occupy infinite channel resources compared to the measurement report of the UE, and the problem that it is difficult to keep the UE and node B measured values consistent in time is avoided. Similarly, if referring to the node B downlink transmit power schemes in soft handover situations proposed in patent application WO01/47145 and patent US6104933, etc., the node B downlink reference transmit power shown in equation (8) can be calculated by the following equation:

if the power distribution is normal, the reference transmission power of each node beta downlink shown in equation (9):fig. 5 describes in detail a method for determining reference power in the downlink power balancing technology under the soft handover condition proposed by the present invention. As shown, when the UE is in a soft handover state, the RNC obtains parameters required to determine downlink reference power of each node B in step 502. According to one embodiment, the RNC can instruct the node Bs involved in the UE soft handover to measure and report the received signal SIR and the transmitted code in a certain manner (e.g., typically repeated at a certain period) through NBAP dedicated measurement signalingAnd (4) power. Alternatively, the RNC can obtain transmit code power from each node B only, while simultaneously obtaining CPICH received signal code power/WCP from the UE_OTCTOr downlink path loss.

In step 504, the RNC decides whether to use a conventional equal power allocation scheme or an optimized power allocation scheme. If the decision at step 504 is "yes", the process proceeds to step 506 where the downlink reference power for each node B is determined according to the aforementioned equation (9) or (14). If the decision at step 504 is "no," the process proceeds to step 508 where the downlink reference power for each node B is determined according to the aforementioned equation (8) or (13).

Then, in step 510, the RNC transmits downlink power including downlink reference power of each node B through a downlink power control command of NBAP

1, each parameter of a balance adjustment loop is respectively sent to each node B participating in the soft handover of the UE, and each node B carries out the power control of the downlink according to the formula (1) according to the adopted downlink power balance adjustment loop algorithm.

The preferred embodiment of the present invention has been described with reference to the WCDMA system, but it should be understood by those skilled in the art that the present invention IS applicable to the CDMA mobile communication system with closed loop power control of the downlink in case of soft handover, which includes but IS not limited to the IS-95 system, the WCDMA system, the CDMA2000 system, and the TD-SCDMA system. And should not be construed as limiting the invention in any way. The present invention may be implemented in software, hardware or a combination of both. Any variations and modifications of the present invention which may occur to those skilled in the art from the foregoing description are intended to be within the scope and spirit of the invention as defined by the appended claims.

Claims

Claims to follow

1. A method of determining a downlink reference power in a soft handover situation, comprising: a first step in which the radio network controller RNC participates in a user equipment

A plurality of node Bs in UE soft handover obtain transmission code power and obtain measurement parameters for reflecting the relative path loss magnitude; and

a second step, in which the RNC determines the downlink reference power P allocated to the UE by the ith node B using the result obtained in the first step under the condition that the current total received power of the UE remains unchanged.
2. The method according to claim 1, wherein the measurement parameters reflecting relative path loss magnitudes include at least one of: is the UE measuring the received signal code power of the common pilot channel CPICH_OTOTDownlink loss measured by the UE and received signal SIR measured by each of the node bs.
3. The method according to claim 1 or 2, characterized in that: the second step comprises determining a downlink reference power ref 'allocated to the UE by the ith node B according to'

Wherein m represents the number of node B participating in soft handoff, i (i = l, 2...., m) node B downlink power allocated by RNC relative to the downlink power of the first node B, and ^ represents the average downlink loss from any one node B participating in soft handoff to the UE, Pj^TXAn estimate representing the current downlink transmit code power of any one of the nodes involved in the soft handover, and wherein the first node B may be set to any one of the plurality of node bs involved in the soft handover.
4. The method according to claim 1 or 2, characterized in that: the second step comprises determining a downlink reference power P that the ith node B allocates to the UE as the ref_mWhere m denotes participation in softeningThe number of node bs involved in the handover, which represents the downlink power ratio of the i (i = l, 2, …, m) th node B allocated by the RNC with respect to the downlink power of the first node B, represents the received signal SIR of any one of the node bs involved in the soft handover, p x represents the estimated value of the current downlink transmit code power of any one of the node bs involved in the soft handover, and wherein the first node B can be set as any one of the node bs involved in the soft handover.
5. The method of claim 3, wherein: the average downlink loss a from the ith node B to the UE is determined by the RNC according to:

_Liwherein; ^ a_cwIndicating the common pilot channel of each node B known to the RNC

Downlink transmit power of CPICH.
6. The method of claim 3, wherein: the downlink average loss a from the ith node B to the UE is determined by the UE according to the formula:

_{Li =}RSCP_CPICHwhere ^ is obtained by the UE through cell broadcast.
7. The method of claim 3, wherein: the RNC is determined according to: s/.

L、 SIR,
8. The method according to claim 3 or 4, characterized in that: "= 1, i = l, 2, …,
9. the method according to claim 3 or 4, wherein the determination of α is made according to the following formula =, i =2, 3, m, < ^ 1.

L、
10. An apparatus for determining a downlink reference power in a soft handover situation, comprising: an obtaining means for obtaining a first step of transmitting code power from a plurality of node bs participating in a soft handover of a user equipment UE and obtaining a measurement parameter reflecting a relative path loss magnitude; and

and a determining device, configured to determine, according to the result obtained by the obtaining device, the downlink reference power P allocated to the UE by the ith node B under the condition that the current total received power of the UE remains unchanged.
11. The apparatus of claim 10, wherein the measurement parameter reflecting the relative path loss magnitude comprises at least one of: the UE measures the received signal code power of the common pilot channel CPICH, WO ^, the UE measures the downlink loss and each node B measures the received signal SIR.
12. The apparatus according to claim 10 or 11, wherein: the determining device determines downlink reference power p 'allocated to the UE by the ith node B according to the following formula'_re/:

Where m represents the number of node Bs involved in soft handover, represents the downlink power ratio of the ith (i = l, 2.. eta., m) node B allocated by the RNC relative to the downlink power of the first node B, and ^ represents the average downlink loss from any one node B involved in soft handover to the UE, p^χAn estimate representing the current downlink transmit code power of any one of the nodes involved in the soft handover, and wherein the first node B may be set to any one of the plurality of node bs involved in the soft handover.
13. The apparatus according to claim 10 or 11, wherein: the determining means determines downlink assigned to the UE by the ith node B according to the following formulaLink reference power p':_c/:

a ∑ IRjP^x

where m denotes the number of node bs involved in soft handover, ", denotes the downlink power ratio of the i (i = l, 2.. said., m) th node B assigned by the RNC with respect to the downlink power of the first node B,.
14. The apparatus of claim 12, wherein: the average downlink loss a from the ith node B to the UE is determined by the RNC according to:

_{L =}RSCP_CP1CHwhere ^ represents the known common pilot channel of each node B

Downlink transmit power of CPICH.
15. The method of claim 12, wherein: the average downlink loss from the ith node B to the UE is determined by the UE according to:

_{L =}RSCP_CPICHwherein ^ wherein_otObtained by the UE through cell broadcast.

PcPICH
16. The apparatus of claim 12, wherein: the average downlink loss from the ith node B to the UE is determined by the RNC according to: in the body fluid of the patient suffering from the disease,

l, SIR, indicating the received signal SIR of the ith node B.
17. The apparatus according to claim 12 or 13, wherein: "= 1, i = l, 2, …, m.
18. The apparatus according to claim 12 or 13, wherein the determination is made according to α, = -i-, i =2, 3, …, m, α, = 1.