WO2003103183A1

WO2003103183A1 - Power based radio resource management

Info

Publication number: WO2003103183A1
Application number: PCT/IB2002/001999
Authority: WO
Inventors: Christian Braun; Kari Pajukoski; Klas Johansson
Original assignee: Nokia Corporation
Priority date: 2002-06-04
Filing date: 2002-06-04
Publication date: 2003-12-11
Also published as: US7317897B2; AU2002309078A1; US20050153660A1

Abstract

The invention relates to a method and a device for power based radio re-sourced management in wireless radio systems with continuously measure-ment of a total interference power Itot and an own-cell interference power Iown as well as a continuous estimation of the system noise power PN and/or the other-to-own cell interference ratio i based on these measurements. Thus, improved values PN and/or i are provided and thus a more accurate load fac-tor/noise rise calculation can be performed.

Description

Power based radio resource management

FIELD OF THE INVENTION

The present invention relates to a method and a device for power based radio resource management in wireless radio systems, such as wireless CDMA systems.

BACKGROUND OF THE INVENTION

In wireless radio systems, such as the third generation (3G) system, radio resource management (RRM) is responsible for utilisation of the air interface resources. RRM is used in order to guarantee the so-called Quality of Service (QoS), to maintain the planned coverage area and to offer high capacity to the users. RRM can be divided into different functionalities, such as handover control, power control, admission control, load control and packet scheduling functionalities. These functions are required to guarantee the Quality of Service and to optimise the system data throughput with a mix of different bit rates, services and quality requirements.

RRM algorithms can be based on the amount of hardware in the network or on the interference levels in the air interface. The case where the hardware limits the capacity before the air interface gets overloaded is called "hard blocking". The case where the air interface load is estimated to be above the planned limit is called "soft blocking". It has been shown that soft blocking based RRM is advantageous as it provides higher capacity than hard blocking based RRM. Therefore, the present invention is concerned with soft blocking based RRM.

In case of utilising soft blocking based RRM, the air interface load needs to be measured. The estimation of the uplink load of the air interface can be based on the wideband received power level or on throughput. The present invention is engaged with load estimation based on wideband received power.

The received power levels can be measured in the base station. Based on such measurements, the uplink load factor η can be obtained. The corresponding calculations are explained hereinafter with reference to Fig. 1.

Fig. 1 shows a base station BS including an antenna 1. For simplicity it is assumed here that one BS equals one cell. The concept can however be extended to cover the case where one BS has several cells. The base station BS receives via the antenna 1 an own-cell interference power l_0Wn from all intra-cell users connected to the base station BS. Furthermore, the base station receives via the antenna 1 an other-cell interference power l_otn from all inter-cell users that are utilizing the same carrier frequency but are connected to other cells than this own cell.

Furthermore, the base station BS receives system noise with a system noise power P_N via the antenna 1 as well as from its own system components, i.e. system noise is at least partly inherent in a base station BS.

The own-cell interference power l_own, the other-cell interference power l_0th, and the system noise power P_N represent the received wideband interference power, called total received power. This can be expressed by the following equation:

The total received power is measured continuously by means of a measurement circuit 3A. The system noise power P_N can be measured by the base station by means of a measurement circuit 2. The system noise power PN is commonly estimated at night, when the load is assumed to be small. Thus, the own-cell interference power l_own and the other-cell interference power l₀ are small as well. This results in

•tot

The thus estimated noise power PN is then used in an RRM controller 3 to perform RRM functionalities, such as load control and admission control.

Unfortunately, this method cannot cope with system noise differences between day and night. Furthermore, this prior art method does not allow to determine the other-to-own cell interference ratio / at all, namely the ratio of the other-all interference power l_oth to the own-all interference power /_ovvn.Thus, rather conservative noise rise targets have to be used in load control. This degrades system performance.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to improve the radio resource management.

This object is achieved by a method for power based radio resource management in wireless radio systems comprising the steps of continuously measuring a total interference power l_tot received at a base station, continuously measuring an own-cell interference power l_owπ of all intra- cell users connected to a predetermined cell, received at said base station, continuously estimating a system noise power PN and/or continuously estimating an other-to-own cell interference ratio / based on a number of consecutive measurements of said total interference power l_tot obtained by said total interference power l_tot measuring step and based on a number of consecutive measurements of said own-cell interference power town obtained by said own-cell interference power l_own measuring step, and performing at least one functionality of said radio resource management based on said estimation of said system noise power P_N and/or said other-to-own cell interference ratio /^'.

Furthermore, the above object is achieved by a device for power based radio resource management in wireless radio systems comprising: means for continuously measuring a total interference power l_tot re- ceived at a base station, means for continuously measuring an own-cell interference power l_0Wn of all intra-cell users connected to a predetermined cell, received at said base station, means for continuously estimating a system noise power PN and/or continuously estimating an other-to-own cell interference ratio / based on a number of consecutive measurements of said total interference power l_tot obtained by said total interference power l_tot measuring means and based on a number of consecutive measurements of said own-cell interference power l_owπ obtained by said own-cell interference power l_own measuring means, and means for performing at least one functionality of said radio resource management based on said estimation of said system noise power P_N and/or said other-to-own cell interference ration /.

The present invention improves the performance of RRM systems, in particular RRM functionalities such as admission control and load control. In power based radio resource management there are two important system parameters related to the uplink (reverse link), namely the other-to-own cell interference ratio / and the system noise power P - Knowledge of these parameters is advantageous for certain RRM functionalities such as load control and admission control. These parameters are very useful for radio network planning and optimisation purposes. The present invention enables an online estimation of the other-to-own cell interference ratio / and the system noise power PN- In particular, as the other-to-own cell interference ratio /^' and the system noise power PN are time varying a robust online estimation of these parameters is desirable. Online knowledge of these parameters is useful for e.g. load estimation and identification of cells with interference problems, e.g. a high other-to-own cell interference ratio /^'.

Due to more exact estimates of system noise power PN, less conservative noise rise targets can be used in load control, which in turn means that a higher capacity can be reached for that particular cell.

The present invention further provides new possibilities to network planning and optimisation, since the interference situation in each cell can be monitored online. Cells with potential problems are easily detected and troubleshooting becomes easier.

When using power based load control, accurate knowledge of system noise power P_N is desirable. Therefore, preferably, the uplink load factor η is continuously calculated as 77 = 1 - ^ / ' t„ot

wherein l_tot is said estimated total interference power and PN is said estimated system noise power.

Alternatively the uplink noise rise NR is continuously calculated as

NR = ^

P_N or as

NR = ¹

1 -

The system noise power PN varies over time. For example, man made noise, e.g. from engines etc., is added to the system noise and can be considerably higher at rush hours than at night. Therefore, preferably, the system noise is estimated online, continuously, in order to allow a more accurate load factor /noise rise calculation. In particular the noise rise NR calculation shows that an accurate system noise power P_N estimation is advantageous as an error in the system noise power P yields an error in noise rise NR.

Further advantageous developments are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention will be described in greater detail based on preferred embodiments with reference to the accompanying drawings, in which: Fig. 1 shows a base station with a power based radio resource management system according to the prior art;

Fig. 2 shows a base station with a power based radio resource management system according to an embodiment of the present invention comprising online estimation of system noise power P_N and other-to-own cell interference ratio /^';

Fig. 3 shows a first embodiment of the online estimation of the system noise power P_N and the other-to-own cell interference ratio / shown in Fig. 2;

Fig. 4 shows a second embodiment of the online estimation of the system noise power PN and the other-to-own cell interference ratio / shown in Fig. 2;

Fig. 5 shows a third embodiment of the online estimation of the system noise power P_wand the other-to-own cell interference ratio / shown in Fig. 2;

Fig. 6 shows a chart illustrating the performance of the system noise power PN estimation; and

Fig. 7 shows a chart illustrating the performance of the other-to-own cell interference ratio /^'.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 has been explained with reference to the prior art in order to explain the background of the invention. Therefore, the above explanations with re- gard to Fig. 1 apply to the invention as well, as far as nothing else is described hereinafter.

Fig. 2 shows a schematic diagram of a base station BS including an antenna 4 for communication between a radio network, such as a UMTS network utilizing wireless CDMA, and user equipment (not shown), e.g. mobile phones or any other mobile devices.

Such a base station BS covers a certain area in order to establish a wireless connection between the base station BS and the user equipment(s) being located within this area. Such an area is defined as a cell.

However, practically, there can be user equipment within a certain cell that is connected with the base station of another cell. Such user equipment causes interference with the signals that are intended for this specific base station BS. Furthermore, user equipment may interfere with this specific base station even though they are not located within the cell of this specific base station BS. These interferences can be regarded as other-cell interference for all inter-cell user equipments that are connected to other cells as far as they are utilizing the same carrier frequency as this specific base station BS. The power of this other-cell interference is defined as other-cell interference power l_oth.

It is noted that l_own and l_0th refer only to interference sources within the same frequency band as the base station BS in question. Interference from sources in other frequency bands may arise due to non-perfect filters. For example, UEs operating on another frequency band may have non-negligible adjacent channel leakage into the frequency band of interest, thus causing interference. This interference is covered in the system noise term, PN, and is one of the reasons for the time-varying nature of PN- Furthermore, all the user equipments connected to this certain cell (hereinafter referred as own-cell) cause an own-cell interference. The own-cell interference power that is received at the base station of this own-cell (the power that is caused by all intra-cell users connected to the own-cell) is defined as l_own- Note that the own cell interference is actually the useful part of the received power, carrying the transmitted user data from the user equipments (UEs).

Furthermore, the base station BS receives background noise, in particular via the antenna 4, and a noise caused by the receiver section of the base station BS, namely the receiver noise. This background noise and the receiver noise as well as any other noise that by occur in such a radio system is defined as system noise with a system noise power P -

The sum of the other-cell interference power l_0th, the own-cell interference power l_own as well as the system noise power PN is hereinafter referred as the total uplink interference power l_tot.

The total uplink interference power l_tot varies over time and is seen by the base station BS at every time instant n as:

l_tot (n) = l_OWn (n) + l_oth(n) + P_N(n)

This total interference power l_t0t(n) is continuously measured by a continuous total interference power l_tot measurement circuit that is comprised in the base station BS.

Furthermore, the base station BS comprises a continuous own-cell interference power lown (n) measurement circuit 6 for continuously measuring the own-cell interference power l_OWn (n). Both measurement circuits 5, 6 continuously provide consecutive measured values l_tot {n) and l_own (n), e.g. every 100 ms. The provided value should reflect the average value over the measurement period. Thus, n can be seen as every measurement reporting instance of the base station BS.

The values of l_tot (n) and l_0Wn (n) are provided to online estimation means 7 that are implemented by software and/or hardware, e.g. by an online estimation circuit. The online estimation means estimates based on the received values hot {n) and l_0Wn {n) the system noise power PN as well as an other-to- cell interference ratio / that is defined as:

Thus, the total interference power hot can be written as

l_tot(n) = l_OWn(n) + i(n)-l_own(n) + P_N = l_own(n)-^ + i(n))+ P_N(n)

The online estimation means 7 assumes that the total interference power l_tot and the own-cell interference power l_own are continuously measured by the base station BS, in particular by the measurements circuits 5, 6 and utilizes these measurements to estimate the other-to-own cell interference ratio / and the system noise power P_N. Fig. 3 illustrates the online estimation circuit 7 of Fig. 2 which is denoted as 307 in Fig. 3. A number of consecutive measurements of the total interference power l_tot and the own-cell interference power l_own is carried out. Thus a system of equations is set up according to:

It t (n) l_own(n)-( i) + P_N l_own{n) 1^' l_0Wn(n + - + i) + P_N O + O 1 ^■(1 + / )^"

l_tot(n + N) l_own(n + N)- ₊ i) ₊ P_N l_own(n + N) 1 This set up of a system of equations is performed by set up system of equation means 308, e.g. by software implementation or by hardware implementation, e.g. by a corresponding circuit.

According to a first embodiment of the online estimation means 7, namely as shown in Fig. 3 as online estimation circuit 307, it is assumed that the other- to-own cell interference ratio / and the system noise power P are fairly constant over the sequence N (independent of n). Thus, the equation system can be solved by means of minimum mean square error method (MSE) that is implemented in equation system solving means 309, either by hardware or by software implementation. Thus, estimates of the other-to-own cell interference ratio / and the system noise power PN are found.

Referring back to Fig. 2 these estimates of the other-to-own cell interference ratio /^' and the system noise power PN are provided to a radio resource management unit 8 that in turn is realized by hardware and/or software implementation. This radio resource management unit 8 performs the functionalities of the radio resource management based on the received estimates of the received system noise power P_N and the other-to-own cell interference ratio /. These functionalities are e.g. load control, admission control, packet scheduling, power control, handover control, load estimation and/or identification of cells with interference problems.

Fig. 4 shows a further embodiment of the online estimation means 7 shown in Fig. 2 being denoted with 407 in Fig. 4. Online estimation means 407 corresponds mainly to online estimation means 307 and thus comprises set up system of equation means 408 and equation system solving means 409. However, the estimates of the system noise power PN and the other-to-own cell interference ratio / are averaged over time in order to get more stable results. Therefore, respective average means 410 for the system noise power estimate PN are provided in order to yield an averaged system noise power value P_N and average means 411 for the other-to-own cell interfer- ence ratio / estimate are provided in order to yield an averaged other-to-own cell interference ratio value / .

Fig. 5 shows a further embodiment of the online estimation means 7 of Fig. 2 being denoted as online estimation means 507 in Fig. 5. Online estimation means 507 is designed in order to provide even better estimates of the signal noise power P_N by using averaged values of the received powers hot (n) and l_own (n) over a predetermined period of time, e.g. 10 s. Further, a corresponding average value of the estimated other-to-own cell interference ratio / is provided as well. In order to achieve this aim, online estimation circuit 507 comprises not only set up system of equation means 508 and equation system solving means 509 which correspond to means 308, 408 and 309, 409 respectively, but also comprises average means 510 for the continuously measured total interference power values hot (n) and own-cell interference power l_0Wn (n) provided by the measurement circuits 5, 6, respectively. Hence, averaged values for the total interference power and the own-cell interference power are provided as l_tot and l_own .

The measured values l_tot(n) and l_0Wn(n) are provided to set up system of equation means 508 which in turn provides its results to equation system solving means 509. Equation system solving means 509 calculates the other- to-own cell interference ratio namely / as described above.

The estimated value for the other-to-own cell interference ratio / is averaged by average means 512 in order to generate an averaged estimated value / for the other-to-own cell interference ratio.

Based on this averaged estimated other-to-own cell interference ratio / and the averaged received powers l_tot and l_own an improved estimate for the sys- tern noise power P_N can be calculated by calculation means 513 as: ^PN = l_tot - l_OWn + i )

wherein l_tot is the average l_M , l_owπ is the average l_owπ and / is the average estimated / over the same time period. The reason why this estimate becomes better is that the error in the estimated /^' is scaled down, since l_own is always smaller than/_to, . Moreover, the fast fluctuating nature of / is averaged out, which gives a more stable performance.

As a result better estimates P_N and / are achieved for the system noise power and the other-to-own cell interference ratio / based on the averaged values l_tot and l_own as well as /^' .

All the above mentioned means comprised in the base station BS and in par- ticular the online estimation means 7, 307, 407 and 507 can be implemented by means of hardware and/or software. In particular, as the above described estimation is not very demanding in terms of computing power and real-time requirements it can be easily implemented in software even though hardware implementation is possible as well.

The performance of the estimation is dependent on the number of measurement samples N used in the minimum mean square error estimation. Even though N may be set arbitrarily, a reasonable value is in the range between 5 and 10.

The performance of the above described system noise power and other-to- own cell interference ratio / estimations have been tested using simulated data from a dynamic WCDMA network simulator. The results are shown in Fig. 6 and 7. Even though the other-to-own cell interference ratio is slightly underestimated, the system noise power estimation is close to the true level. Fig. 6 shows the performance of the system noise power estimation P_N. Each value plotted is derived using the average of all previous power measurements. The system noise power estimation converges to about -100.74 dBm, while the true system noise power was -100.9 dBm (constant), i.e. the noise power was overestimated by 0.16 dB. The uplink average noise rise in this simulation was 2.3 dB. N=10 consecutive measurements were used for every new estimate of the other-to-own cell interference ratio /^'.

Fig. 7 shows the other-to-own cell interference ratio / estimation. N=10 consecutive measurements were used for every new estimation of the other-to- own cell interference ratio and the result is filtered with an MR filter with forgetting factor alpha = 0.1. The average estimated other-to-own cell interference ratio /was 0.32 whereas the true value was 0.43.

It is noted that the present invention is not restricted to the preferred embodiments described above. In particular, the above described estimations can be performed in the radio network controller (the equipment in e.g. a radio network subsystem for controlling the use and the integrity of the radio resources) as well. Thus the estimation have not necessarily to be performed in the base station. Both, the base station as well as the radio network controller comprise a radio resource management functional part which is suitable to implement the above described estimations. Thus, the preferred embodiments may vary within the scope of the attached claims.

Claims

1. A method for power based radio resource management (8) in wireless radio systems comprising the steps of continuously measuring (5) a total interference power (l_tot ) received at a base station (BS), - continuously measuring (6) an own-cell interference power (/_{o vπ}) of all intra-cell users connected to a predetermined cell, received at said base station (BS), continuously estimating (7) a system noise power (PN) and/or continuously estimating (7) an other-to-own cell interference ra- tio (i) based on a number of consecutive measurements of said total interference power (l_tot) obtained by said total interference power (hoi) measuring step (5) and based on a number of consecutive measurements of said own-cell interference power (l_own) obtained by said own-cell interference power (l_0Wn) meas- uring step (6), and performing (8) at least one functionality of said radio resource management based on said estimation (7) of said system noise power (PN) and/or said other-to-own cell interference ratio (/).

2. A method according to claim 1 , wherein said functionality comprises load control, admission control, packet scheduling, power control, handover control, load estimation, and/or identification of cells with interference problems.

3. A method according to claim 1 or 2, wherein said system noise power (P_N) being received at said base station (BS) as well as being inherent in said base station (BS).

4. A method according to any one of the preceding claims, wherein said other-to-own cell interference ratio (/) is defined as the ratio of an other-cell interference power (l₀th) of all inter-cell users connected to other cells than said predetermined cell utilizing the same carrier frequency as said predetermined cell to said own-cell interference power

(•own).

5. A method according to any one of the preceding claims, wherein an uplink load factor η is continuously calculated as

wherein h_ot is said estimated total interference power and PN is said estimated system noise power.

6. A method according to any one of the preceding claims, wherein an uplink noise rise NR is continuously calculated as

NR = ≡-

or as

NR =

1 - /7

wherein h_ot is said estimated total interference power, PN is said estimated system noise power and η is said uplink load factor. A method according to any one of the preceding claims, wherein said estimating step

(7) uses a sequence of N+1 consecutive measurements and comprises the step of setting up a system of equations according to:

U") l₀wn(n)- (l + i) + P_N l_own(n) ϊ /«(n + 1) l_OWn(n + V- V + 0 + P_N /„w + ) 1 ^'(1 + 0

l_u{n + N) l_own(n + N)- ₊ i) ₊ P_N l_own(n + N) 1

wherein n is a measurement reporting instance and N is an integer value.

8. A method according to claim 7, wherein said estimating step (7) further comprises the step of solving the system of equations (309, 409, 509, 509) by using the minimum mean square error method.

9. A method according to claim 7 or 8, wherein N is an integer value in the range of 5 to 10.

10. A method according to any one of the preceding claims, wherein said estimated system noise power (P_N) and said estimated other-to-own cell interference ratio (/) are averaged (410, 411 ) over time, respectively.

11. A method according to any one of the preceding claims, wherein a system noise power (PN) estimate is calculated (512) as

P_w = >_to( - owπ (1 + ' ) wherein l_tot is an average value of the total interference power (l_tot), wherein l_own is an average value of the own-cell interference power

(lown), and wherein / is an average value of the estimated other-to- own cell interference ratio (/).

12. A method according to claim 11 , wherein all average values are calculated over the same time period.

13. A method according to any one of the preceding claims, wherein said method being implemented in a radio resource management functional part of said base station (BS).

14. A method according to any one of claims 1 to 12, wherein said method being implemented in a radio resource management functional part of a radio network controller.

15. A method according to any one of the preceding claims, wherein said wireless radio system being a code division multiple access (CDMA) system.

16. A device for power based radio resource management (RRM) in wireless radio systems comprising: means (5) for continuously measuring a total interference power (h_ot) received at a base station (BS), - means (6) for continuously measuring an own-cell interference power (lown) of all intra-cell users connected to a predetermined cell, received at said base station (BS), means (7) for continuously estimating a system noise power (P_N) and/or continuously estimating an other-to-own cell inter- ference ratio (/) based on a number of consecutive measurements of said total interference power (h_oi) obtained by said to- tal interference power (/_to,) measuring means (5) and based on a number of consecutive measurements of said own-cell interference power (lown) obtained by said own-cell interference power (lown) measuring means (6), and - means (8) for performing at least one functionality of said radio resource management (RRM) based on said estimation of said system noise power (PN) and/or said other-to-own cell interference ratio (/).

17. A device according to claim 16, wherein said device further comprises means for performing a method according to any one of claims 2 to 15.