WO2002091781A1

WO2002091781A1 - Method and device for controlling admission of users to a cellular radio network

Info

Publication number: WO2002091781A1
Application number: PCT/EP2001/007647
Authority: WO
Inventors: Albert HÖGLUND; Janne PÖLLÖNEN; Laiho Jaana
Original assignee: Nokia Corporation
Priority date: 2001-05-03
Filing date: 2001-05-03
Publication date: 2002-11-14

Abstract

The present invention relates to a method and a cellular radio network device (3) for controllingg the admission of user (4, 6) to a cellular radio netwok (1). In order to determine how much traffic is allowed in a cell (2), threshold values are autotuned using quality measurements gathered during high load on a link. Thus, the network capacity is in increased while fulfilling desired quality requirements.

Description

Method and device for controlling admission of users to a cellular radio network

FIELD OF THE INVENTION

The present invention relates to a method and a cellular radio network device for controlling the admission of users to the cellular radio network.

BACKGROUND OF THE INVENTION

In cellular radio systems, such as in WCDMA (Wideband Code Division Multiple Access) or UMTS (Universal Mobile Telecommunications System) systems information is transferred between a network device and a user, such as a mobile terminal, by transmitting signals.

These signals may be distorted on their way from a transmitter to a receiver. Thereby e. g. a modulator of a transmitter, means of transmission, i. e. radio waves, interference sources, fading and demodulator of a receiver have distorting influence on the signals. These factors form a so-called channel. Each base station has a plurality of channels at its disposal. On each channel information is transferred between the base station and the users, thus establishing a connection between a user and the base station. The base station decides whether to admit new users depending on the number of such connections or on the workload of the network. This process of decision is called admission control.

In WCDMA power based admission control can be used in both, uplink and downlink. In uplink there is a cell based threshold for received channel power level. Correspondingly in downlink there is a cell based threshold for transmitted channel power level. These thresholds are used to determine whether to admit a new user or not. Accordingly these threshold values are used to determine how much traffic is allowed in a cell of the cellular radio network. Thereby it is important to select the correct thresholds. If the threshold values are too low, not all of the capacity of the cellular radio network is utilized. On the other hand, if the threshold values are too high, too many connections are admitted in a particular cell. Thus, the interference increases causing bad quality of the connections between the users and the network, in particular of calls. This is caused by power outage of mobile terminals in uplink and in downlink connections that hit the maximum specific transmission powers, reducing the coverage of the specific cell and making the quality of calls worse.

It is known to manually correct the threshold values. However, as the number of cells in a network is very high, in particular more than 10,000, manual correction is a very time-consuming and difficult task.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to improve the correction of such threshold values.

This object is achieved by a method of admission of users to a cellular radio network , comprising the steps of determining a threshold value for a quantity to be measured, measuring said quantity in order to obtain a measured value, comparing said measured value with said threshold value, and deciding whether to admit a new user based on the result of said comparison, thereby autotuning said threshold value using quality measurements in order to define a required quality of a link, uplink or downlink, said quality measurements being gathered during high load and said link. Furthermore the above object is achieved by a cellular radio network device for performing that method, namely a cellular radio network device for controlling the admission of users to a cellular radio network, comprising means for determining a threshold value for a quantity to be measured, means for measuring said quantity in order to obtain a measured value, means for comparing said measured value with said threshold value, means for deciding whether to admit a new user based on the result of said comparison, means for autotuning said threshold value using quality measurements in order to define a required quality of a link, uplink or downlink, and means for quality measurements gathered during high load on said link.

Accordingly, the uplink power threshold of a cell is autotuned using quality measurements gathered during high uplink load. The downlink power threshold of a cell is correspondingly autotuned using quality measurements gathered when the cell has been under high downlink load. The thresholds are autotuned so that they are as high as possible while the quality criteria are fulfilled.

In case of poor or degraded quality of link the threshold value is autotuned towards a direction which improves the situation and in the case of high load and better quality of connections than required, the threshold value is autotuned in a direction which increases capacity of the network. Thus, the network capacity is maximized while fulfilling the quality requirements. A capacity quality trade-off can be performed by adjusting the quality criteria. By allowing poorer quality the capacity is increased, thus in particular a higher throughput and/or lower blocking of calls is enabled, while it is correspondingly decreased by requiring very high quality.

The invention is applicable to power based admission control as well as to throughput based or connection based admission control. The corresponding thresholds can thus also be expressed in power units as well as in other than power units: for example throughput units, e.g. kbit/s. In each case it is possible to use quality criteria to maximize the load level throughputs. All methods are able to provide an equivalent Capacity-Quality tradeoff.

The invention enables the optimising of cell-specific thresholds. Commonly, the optimal threshold values vary from cell to cell depending on the radio propagation environment of the cell. In some cells where the propagation environment is good, there is more room for increasing the thresholds to allow more users in the cell, because in this kind of cells the quality of calls does not decrease much when the thresholds are increased. In other cells that have poor propagation environment, the power thresholds should be kept at somehow lower level to meet the quality requirements of the cell. As the different environment of the cells is difficult to take into consideration by static planning of a radio network, the invention in particular overcomes these problems by using a real time monitoring. This is particularly useful, since the thresholds can change over time.

Thus, the invention allows to avoid inaccurate or even incorrect threshold values. Moreover, the invention provides correct cell-specific uplink and downlink (power) threshold values. Thus, the capacity of the network is increased, since usually a network is initially set with (power) threshold values at a too low level to make sure that the required quality criteria are achieved. However, sometimes in a network the (power) threshold values might also be set too high, which results in too high interference (noise) level in a cell causing poor quality of links. This case, according to the invention the thresholds are reduced in order to achieve a quality of a required level.

Preferably, the quality requirements are the actual number of dropped, blocked and/or bad calls and/or the ratio of dropped, blocked and/or bad calls to a total amount of calls; a data throughput of actual transmitted data in uplink and/or downlink; an average frame error rate of defective data frames; delay times of transmitted data packets; and/or retransmission rates of retransmitted data packets due to defective data. The blocked call, the throughput as well as the packet traffic delay criteria improve as the target threshold value is increased and degrade as the target is decreased.

Preferably, the quality of a link is determined by a cost function, said cost function taking into account at least two, more than two or all of the above mentioned quality of link representations, thereby weighing each of the representations. Such a cost function thus describes the quality requirements. It can be minimized by adjusting the target value. As an example a dropped call can be several, e.g. 10 times more severe than a blocked call.

Preferably, quality requirements are drop call or bad call ratios below a certain percentage. The quality of a call can e.g. be considered bad if it's average frame error ratio (FER) is above a certain percentage, which is clearly higher than the outer loop FER-target (e.g. average FER above 2% in case of 1% FER-target). An average FER clearly higher than the FER-target means that the mobile device/devices suffer from power outage in uplink and BS (Base Station) from link power outage in downlink. Additionally with packet switched traffic delay and retransmission rates are preferably used for quality measurements. Different traffic classes have different quality criteria, though. For example, the traffic classes in UMTS are: conversational, streaming, interactive, and background. Normally some of the quality classes are less sensitive to poor quality (e.g. background). The traffic classes to be preferably monitored are selected, e.g. conversational and streaming, and then the quality requirements in these classes are satisfied in the method. In uplink the main bitrate to be preferably monitored is the bitrate that has been planned to have coverage in the whole cell area (e.g. 144 kb/s). In downlink preferably all bitrates are monitored, since in downlink link power limits are scaled using bitrates and planned Eb/No-values, Eb being the energy per bit and No being the noise power density.

In the autotuning of threshold values it is desired to cope with the mobility of the mobile devices. Therefore, it is advantageously desired to associate to a cell only quality measures of that parts a call that the call is connected to the cell in question. Thereby, poor quality in neighbouring cells is suppressed in order not to affect the autotuning of power thresholds in a cell. Furthermore preferably diversity handover issues are taken into account while evaluating the quality of calls. A possible addition before raising the power threshold in a cell is to check if adjacent cells are suffering from poor quality. If this is the case then it is better not to raise the power threshold.

Summarized, due to invention the network capacity is maximized while fulfilling the quality requirements. Furthermore, due to the invention operability and optimisation is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention will be described in greater detail based on an preferred embodiment with reference to the accompanying drawings, in which:

Fig. 1 shows a cellular radio network;

Fig. 2 shows the autotuning of an uplink power threshold value;

Fig. 3 shows the autotuning of a downlink power threshold value; and

Fig. 4 shows a diagram of specific elements of a cellular radio network device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Fig. 1 illustrates a cellular radio network 1 comprising a number of cells 2 adjoining to each other. Each cell 2 is radio covered by a network device 3 for connecting users 4 or mobile devices to the network 1. The users 4 are each connected via respective radio connections 5 to the network 1.

It should be noted that the network device 3 in this example comprises admission control functionality. However the admission control may be implemented also in some other device in some other cell 2. In UMTS networks the admission control is located in RNC (radio network controller) which is controlling many base stations which are connected to the users' 4 user equipments. The admission control may be implemented also in the base stations. The radio interference between network device 3 (base station) and user 4 (user equipment) is implemented preferably by using CDMA technique (including WCDMA).

This method is applicable independent of the location of the admission decision. Admission decision can also be distributed in several network elements . Admission control is preferably performed at:

RAB (Radio Access Bearer) establishment,

RAB renegotiation,

Handover.

Admission control is in particular responsible for: radio bearer parameter selection (must include new shared channel parameters), and radio bearer QoS (Quality of Service) negotiation and renegotiation. In particular it finds out if there are cell resources available. This may be taken as the actual admission.

The parameters related to admission control are preferably:

RAB (Radio Access Bearer) QoS parameters (core network), - Cell capability (OMS),

MS (mobile station) capability (core network),

Cell measurements: load, interference (BTS - Base Transceiver Station), Load information from NRT users (PS),

MS measurements, dl interference, neighbour cell measurements (MS),

PDCP (Packet Data Convergence Protocol)/RLC (Radio Link Control) resources (BSGW), - GERAN: frequency and TSL specific idle channel interference, used in

DFCA (neighbour CRS),

GERAN: multi carrier power amplifier (MCPA), cell total transmitted power

(BTS), and/or

PDCP/RLC resources (reported periodically by BSGW).

Admission control functionalities locations are preferably as follows: UCF makes the AC decision and takes care of signaling. RNAS selects BSGW and RNGW. UCF selects the L2/L1 parameters that are not dependent on the cell status. CRS makes admission control for physical resources. CRS selects the L2/L1 parameters that are related on the cell status.

If a new user 6 intends to establish a connection 5 with the network 1 the network device 3 decides whether to admit the new user 6 to the network 1 or not.

If a certain threshold value, in particular a power threshold value would be exceeded in case of admittance, the new user 6 is rejected. Accordingly, the new user 6 is admitted to the network 1 , in case of the power threshold value not being exceeded in case of admittance.

In order to perform the decision, whether or not to admit a new user, an actual power value is measured, the increased power value in case of admittance is estimated and compared with the power threshold value.

According to the preferred embodiment of the present invention, the threshold value is not constant, but varies depending on quality requirements of the respective link, namely the uplink or downlink. These quality requirements are gathered during high link load of the respective link.

Figure 2 shows the adjustment of cell uplink power threshold. In step 100 it is evaluated whether the uplink quality requirements are better than a predetermined value under high uplink load. This predetermined value is calculated by a fixed value, called "requirements" added by a difference value, called "delta". Binomial confidence intervals can be used to determine delta. E.g. a delta equaling two binomial standard deviations would correspondingly mean that the probability of a quality different than the requirements is 95%.

In case of the uplink quality requirements being better than "requirements + delta" in step 101 the cell uplink power threshold is increased by a certain value upStepSize, e.g. 0.3 dB.

After increasing the uplink power threshold in step 101 the procedure returns to step 100.

However, if in step 100 the uplink quality requirements are not better than "requirements + delta" under uplink high load, the procedure turns to block 102 evaluating whether the uplink quality requirements are worse than a further predetermine value, called "requirements-delta", calculated by subtracting "delta" from "requirements". Correspondingly as in the uplink case binomial confidence intervals can be used to determine delta.

If the uplink quality requirements are not worse than "requirements - delta" under uplink high load the procedure turns from step 102 back to step 100 performing the above described evaluation in step 100.

However, if the uplink quality requirements are worse than "requirements - delta" under uplink high load, according to Step 103 it is further evaluated if the total throughput is higher than a predetermined value calculated by a fixed bitrate requirement value, called "bitrate requirements" added by further difference value, called "beta", thus generating a value called "bitrate requirements + beta". Additionally the blocking rate should be below "blocking rate requirement - gamma". Binomial confidence intervals can be used to determine gamma and e.g. Gaussian confidence intervals to determine beta.

If the total bitrate is not higher than "bitrate requirements + beta" the procedure returns back to step 100 performing the above described evaluation.

However, if in step 103 it is evaluated that the total bitrate is higher than "bitrate requirements + beta", in step 104 the cell uplink power threshold is decreased by a predetermined value, namely by downStepSize.

After performing the adjustment of the power threshold according to Step 104, it is continued with step 100 as described above.

The adjustment of a cell downlink power threshold is described hereinafter:

Figure 3 shows the adjustment of cell downlink power threshold. In step 200 it is evaluated whether the downlink quality requirements are better than a predetermined value under downlink high load. This predetermined value is calculated by a further fixed value, called "requirements" added by a further difference value, called "delta".

In case of the downlink quality requirements being better than "requirements + delta" in step 201 the cell downlink power threshold is increased by a certain value upStepSize.

After increasing the downlink power threshold in step 201 the procedure returns to step 200. However, if in step 200 the downlink quality requirements are not better than "requirements + delta" under downlink high load, the procedure turns to block 202 evaluating whether the downlink quality requirements are worse than a further predetermine value, called "requirements - delta", calculated by subtracting "delta" from "requirements".

If the downlink quality requirements are not worse than "requirements - delta" under downlink high load the procedure turns from step 202 back to step 200 performing the above described evaluation in step 200.

However, if the downlink quality requirements are worse than "requirements - delta" under downlink high load, according to Step 203 it is further evaluated if the total bitrate is higher than a predetermine value calculated by a fixed bitrate requirement value, called "bitrate requirements" added by further difference value, called "beta", thus generating a value called "bitrate requirements + beta". Additionally the blocking rate should be below "blocking rate requirement - gamma". Binomial confidence intervals can be used to determine beta and gamma.

If the total bitrate is not higher than "bitrate requirements + beta" the procedure returns back to step 200 performing the above described evaluation.

However, if in step 203 it is evaluated that the total bitrate is higher than "bitrate requirements + beta", in step 204 the cell downlink power threshold is decreased by a predetermined value, namely by downStepSize.

After performing the adjustment of the power threshold according to Step 204, it is continued with step 200 as described above.

Furthermore, an actual load value of the uplink and/or downlink is determined. This actual load value is compared with a predefined load value in order to determine high load. Thereafter a quality measurement is performed if said actual load value exceeds the predefined load value, i.e. if high load has been determined. Thus, critical requirements during high load are detected.

Figure 4 shows a block diagram of components of a cellular radio network device 3 for performing the above described method.

The device 3 comprises a unit 7 for determining and/or storing a power threshold value as well as the unit 8 for measuring a power value. Unit 8 may comprise also means for averaging short term power levels. Both units 7 and 8 are connected with a comparator 9 for comparing the measured power value with the power threshold value.

The comparator 9 is connected to a decision unit 10 which is deciding whether to admit a new user to the network. The decision is made on the basis of the result of the comparison performed by comparator 9.

Furthermore, an autotuning unit 11 is provided for autotuning the threshold value using quality measurements in order to define a required quality of a link, namely uplink or downlink, and a quality measurement unit 12 for quality measurements gathered during high load on uplink or downlink.

Furthermore, an adjustment circuit 13 is provided with the autotuning unit 11 for increasing the threshold value if an actual quality of the link is better than the required quality of the link or decreasing the threshold value if the actual quality of the link is worse than the required quality of the link, in particular if a total throughput of the link is higher than a required bitrate and the blocking rate is lower than a blocking criteria.

In the above described embodiment high load can be determined as follows: A normal criteria for high load could be that the average received and/or transmitted power of the channel has an average value within a certain, preferably predetermined margin, in particular within a 0.5 dB margin of the power threshold. If the power threshold for some reason has been set too high, it means that the system still can suffer from bad quality but does not reach the high load state. In practice this is not a problem. However, preferably a possibility is provided to check quality for looser high load situations (threshold -1dB, threshold -1.5dB, threshold -2dB) if high load state is newer reach. If it is reached and quality is poor the high load criteria can be increased again, but if it is poor the power threshold can be lowered.

It is noted that the above described algorithm can be performed either in an automatic mode or a manual mode. In the manual mode an operator decides whether to accept the suggested changes or not. In this case the implementation of the algorithm is preferably located near RNC (radio network controller) or the network management system. In the automatic mode the location is preferably the RNC. In future IP RAN (Remote Access Network) networks some RNC functionalities are located in the base stations and the admission control functionalities may also be located in the base stations or distributed to the radio access network. It is noted that the present invention is not restricted to the preferred embodiment described above. In particular the thresholds can be additionally used for further purposes as for how to schedule packets. The power or throughput thresholds set the limits for the amount of packets that can be scheduled. The preferred embodiment may thus vary within the scope of the attached claims.

Claims

1. A method for controlling the admission of users (4, 6) to a cellular radio network (1 ), comprising the steps of: determining (7) a threshold value (cell uplink/downlink power threshold) for a quantity (power level) to be measured, measuring (8) said quantity (power level) in order to obtain a measured value, comparing (9) said measured value with said threshold value (cell uplink/downlink power threshold), and deciding (10) whether to admit a new user (6) based on the result of said comparison (9), thereby autotuning (11) said threshold value (cell uplink/downlink power threshold) using quality measurements in order to define a required quality of a link, uplink or downlink, said quality measurements being gathered during high load on said link.

2. A method according to claim 1 , wherein said threshold value (cell uplink/downlink power threshold) being a channel power threshold value indicating a maximum admissible received channel power level in uplink, and/or a maximum admissible transmitted power level in downlink, and said quantity to be measured being a channel power level of received power in uplink and/or a channel power level of transmitted power in downlink.

3. A method according to claim 1 and 2, wherein said threshold value being a throughput threshold value indicating a maximum admissible data throughput in uplink and/or downlink, and said quantity to be measured being a throughput level of received data in uplink and/or a throughput level of transmitted data in downlink.

4. A method according to any one of the preceding claims, wherein said threshold value being a connection (5) threshold value indicating a maximum admissible number (5) of connections between users (4) and said network (1), and said quantity to be measured being a actual number of connections (5).

5. A method according to any one of the preceding claims, wherein said quality of a link is represented by a) the actual number of dropped, blocked and/or bad calls and/or the ratio of dropped, blocked and/or bad calls to a total amount of calls, b) a data throughput of actual transmitted data in uplink and/or downlink, c) an average frame error rate of defective data frames, d) delay times of transmitted data packets, and/or e) retransmission rates of retransmitted data packets due to defective data.

6. A method according to claim 5, wherein said quality of a link is determined by a cost function, said cost function taking into account at least two, more than two or all of the quality of link representations, thereby weighing each of said representations.

7. A method according to any one of the preceding claims, thereby determining an actual load value of said link, comparing said load value with a predefined load value in order to determine high load, and performing a quality measurement if said actual load value exceeds the predefined load value.

8. A method according to any one of the preceding claims, wherein said autotuning is performed by increasing said threshold value (101 , 201 ) if an actual quality of said link is better than said required quality of said link (100, 200).

9. A method according to any one of the preceding claims, wherein said autotuning is performed by decreasing said threshold value (104, 204) if said actual quality of said link is worse than said required quality of said link (102, 103).

10. A method according to claim 9, wherein said decreasing (104, 204) is performed if a total bitrate of said link is higher than a required bitrate (103).

11. A method according to claim 9 or 10, wherein said decreasing ( 04, 204) is performed if a blocking rate is below a blocking rate criteria (103).

12. A method according to any one of the preceding claims, wherein said threshold value is autotuned as high as possible while fulfilling said required quality of said link.

13. A method according to any one of the preceding claims, wherein said required quality is defined depending on traffic classes, so that different traffic classes have different required qualities.

14. A method according to any one of the preceding claims, wherein data packets are scheduled depending on said threshold value (cell uplink/downlink power threshold).

15. A method according to any one of the preceding claims, wherein said autotuning is performed continuously in order to allow real time monitoring.

16. A method according to any one of the preceding claims, wherein said autotuned power or throughput thresholds are used in/for packet scheduling.

17. A cellular radio network device for controlling the admission of users to a cellular radio network (1), comprising: means (7) for determining a threshold value (cell uplink/downlink power threshold) for a quantity to be measured, means (8) for measuring said quantity (power level) in order to obtain a measured value, means (9) for comparing said measured value with said threshold value, means (10) for deciding whether to admit a new user (6) based on a result of said comparing means (9), - means (11 ) for autotuning said threshold value (cell uplink/downlink power threshold) using quality measurements in order to define a required quality of a link, uplink or downlink, and means for quality measurements (12) gathered during high load on said link.

18. A device according to claim 17, said means for autotuning comprising means for adjusting (13) said threshold value (cell uplink/downlink power threshold), namely increasing (101 , 201 ) said threshold value (cell uplink/downlink power threshold) if an actual quality of said link is better than said required quality of said link (100, 200), or decreasing (104, 204) said threshold value (cell uplink/downlink power threshold) if said actual quality of said link is worse than said required quality of said link (102, 202), in particular if a total bitrate of said link is higher than a required bitrate (103, 203).

9. A device according to claim 17 or 18 comprising means for performing a method according to any of claims 2 to 16.