WO2010133256A1

WO2010133256A1 - Load balancing in communications networks with mobile station decided handover

Info

Publication number: WO2010133256A1
Application number: PCT/EP2009/056212
Authority: WO
Inventors: Sandro Grech; Roman Pichna
Original assignee: Nokia Siemens Networks Oy
Priority date: 2009-05-22
Filing date: 2009-05-22
Publication date: 2010-11-25

Abstract

A load of an apparatus of a communications network is evaluated and handover parameters to be advertized for mobile station decided handover are adapted accordingly. Moreover, radio resource management information may be exchanged between the apparatus and at least one neighboring apparatus in the communications network, and a load of the at least one neighboring apparatus may be evaluated from the exchanged radio resource management information. The handover parameters to be advertized may be adapted in case the evaluated load of the apparatus and the evaluated load of the at least one neighboring apparatus have reached predetermined limits. As a result, mobile stations of a communications network system are provided with modified handover parameters which induce the mobile stations to make a handover decision as desired by a network infrastructure.

Description

Load Balancing in Communications Networks with Mobile Station decided Handover

The present invention relates to load balancing in a communications network, and in particular to load balancing in a communications network with MS (mobile station) decided HO (handover) .

Load balancing is an important feature for radio resource management. In particular, in a communications network with cellular technology load balancing between cells or between sectors in a network with tiered underlay/overlay cellular network topology is a challenge.

In communication environments with network centric radio resource management and handover decision making in a network infrastructure, load balancing is controlled by handover decisions made in the network infrastructure and handover commands sent to mobile stations.

However, in communication environments such as WiMAX (Worldwide Interoperability for Microwave Access) , networks with de-central structure where a handover comprises a mobile based solution, e.g. MS to MS communications, or fourth generation networks, a handover decision is upon the mobile station.

The present invention aims at providing load balancing in communications networks where HO decision is left upon mobile stations.

According to an embodiment of the invention, a load of an apparatus of a communications network is evaluated and handover parameters to be advertized for mobile station de- cided handover are adapted accordingly. Moreover, radio resource management information may be exchanged between the apparatus and at least one neighboring apparatus in the communications network, and a load of the at least one neighboring apparatus may be evaluated from the exchanged radio resource management information. The handover parameters to be advertized may be adapted in case the evaluated load of the apparatus and the evaluated load of the at least one neighboring apparatus have reached predetermined limits. As a result, mobile stations of a communications network system are provided with modified handover parameters which induce the mobile stations to make a handover decision as desired by a network infrastructure.

The present invention may be implemented by an apparatus, a method and a computer program product as defined in the appended claims.

In the following embodiments of the invention are described with reference to the accompanying drawings, in which:

Fig. 1 shows a schematic block diagram illustrating a communications network system comprising apparatuses according to an embodiment of the invention;

Fig. 2 shows a flow chart illustrating a load distribution procedure according to an embodiment of the invention;

Fig. 3 shows a chart illustrating a function relating load metric and HO trigger according to an example of an embodiment of the invention;

Fig. 4 shows a schematic diagram illustrating an example in which handover results in a larger overall resource consumption; and Fig. 5 shows time charts illustrating changes of trigger values over time according to an example of an embodiment of the invention.

As shown in Fig. 1 illustrating an embodiment of the invention, an apparatus 100a comprises a processor 110a, an interface 120a and a transceiver 130a, which are linked by a bus 140a.

Similarly, an apparatus 100b comprises a processor 110b, an interface 120b and a transceiver 130b, which are linked by a bus 140b.

The apparatuses 100a and 100b may be base stations (BS) of a communications network. The communications network may comprise a plurality of apparatuses 100a, 100b. According to an example of an embodiment of the invention, the communications network comprises a WiMAX environment.

Fig. 1 further shows mobile stations 200a and 200b which may communicate with the apparatuses 100a and 100b. The mobile stations 200a and 200b are part of a communications network system which may comprise the communications network in which the apparatuses 100a and 100b are located.

The transceivers 130a, 130b may transmit handover parameters, which may trigger initiation of handovers in the mobile stations 200a, 200b.

The interfaces 120a, 120b may exchange radio resource management (RRM) information of the apparatuses 100a, 100b, including information such as spare capacity of the apparatuses 100a, 100b. The processor 110a may evaluate a load of the apparatus 100a, and adapt handover parameters to be advertized for mobile station decided handover in case the evaluated load has reached a predetermined limit. The load of the apparatus 100a may comprise an average percentage of frame resources utilized in a given number of past frames. The limit may comprise a given load of the apparatus 100a.

The processor 110a may further evaluate a load of apparatus 100b from the exchanged radio resource management information, and adapt the handover parameters to be advertized in case the evaluated load of the apparatus 100a and the evaluated load of the apparatus 100b have reached predetermined limits. The load of the neighboring apparatuses 100a and 100b may comprise a frame utilization rate. The predetermined limits may comprise measures of a load distribution between the apparatus 100a and the apparatus 100b.

While Fig. 1 shows apparatus 100a and apparatus 100b as neighboring apparatuses, there may be a plurality of neighboring apparatuses.

As shown in Fig. 2 illustrating a load distribution procedure according to an embodiment of the invention, in step S301 radio resource management (RRM) information is exchanged between apparatuses, e.g. neighboring base stations, which may include spare capacity of the neighboring base stations, for example.

In step S302 loads of the neighboring base stations are evaluated.

In step S303 it is determined whether predetermined limits have been reached. If yes, handover trigger parameters are adapted in step S304 and the process returns to step S301. If the predetermined limits have not been reached, the process returns to step S301.

A load distribution between the neighboring base stations may be determined from the radio resource management information. The determined load distribution may indicate the predetermined limits for the neighboring base stations. These procedures may be performed by the processor 110a for apparatus 100a and by the processor 110b for the apparatus 100b as described above with respect to Fig. 1.

According to an embodiment of the invention, to adapt a rate of hand-outs of mobile stations from a base station to a load or relative load distribution between base stations, a base station can modify advertized HO parameters as a function of load or relative load distribution between base stations .

For example, in WiMAX, a base station supports RSSI (Received Signal Strength Indicator) , CINR (Carrier to Interference and Noise Ratio) and RTD (Round-Trip Delay) HO triggers for MS-initiated handovers. The MS HO procedure is assisted by advertising HO triggers that determine when specific HO actions are taken by a mobile station. The base station can advertise RSSI, CINR and RTD triggers that determine when the mobile station should send a neighbor scanning request, neighbor scanning report or handover request. The base station advertises common triggers for all neighboring base stations in a DCD (Downlink Channel Descriptor) MAC message broadcast, for example.

According to an embodiment of the invention, HO triggers advertised by the base station may be adapted dynamically as a function of relative loads between the base station and its neighboring base stations. In other words, handover parameters to be advertized may be adapted in accordance with a function of the loads of the neighboring apparatuses. This procedure may be performed by the processor 110a for apparatus 100a and by the processor 110b for the apparatus 100b.

Fig. 3 shows a chart illustrating adaptation of HO trigger based on Load_metric according to an example of an embodiment of the invention.

The Load_metric in Fig. 3 may be one or a combination of the following:

- The Load_metric comprises only a load of a base station currently serving a mobile station (serving base station, S-BS), for example the apparatus 100a in Fig. 1. For example, the load of the serving base station comprises an average percentage of frame resources utilized in a given number of frames in the past.

- The Load metric comprises load of the S-BS and M neighboring base stations, wherein the load may comprise a frame utilization rate of the M neighbors.

- The Load metric comprises a ratio of loads of the S-BS and a target base station (T-BS) to which handover of the mobile station is to be induced.

According to an example of the invention, the function may be configured to induce handover to at least one specific base station of the M neighboring base stations. For example, only a least loaded neighboring base station may be selected, to which handover of the mobile station is to be induced. The above-described Load_metrics may be weighted to bias the function for specific base stations, e.g., selecting only the least-loaded T-BS to which handover of the mobile station is to be induced, instead of all less loaded neighboring base stations. According to an embodiment of the invention, a base station may minimize an overall network resource consumption due to load balancing between base stations by rejecting handover request from selected mobile stations.

When adapted handover parameters are transmitted, e.g. by the transceiver 130a shown in Fig. 1, an overall radio network resource consumption resulting from accepted handover requests which are based on the transmitted adapted handover parameters may be estimated e.g. by the processor 110a shown in Fig. 1. At least one of the accepted handover requests may be rejected based on the estimated overall radio network resource consumption e.g. by the processor 110a shown in Fig . 1.

Fig. 4 shows a schematic diagram illustrating an example with handover resulting in larger overall resource consumption .

A serving base station S-BS broadcasts new handover thresholds, i.e. the adapted handover parameters.

Mobile stations MSl and MS2 served by the S-BS report scanning results, e.g. CINR (or RSSI) as estimated by MSl and MS2 from a neighboring base station T-BS. These estimates are indicative of the modulation and coding scheme (MCS) to be likely used after handing over to the T-BS.

The mobile stations MSl and MS2 initiate a handover procedure, e.g. using a MOB_MSHO_REQ (MS-initiated HO request) message, or the communications network initiates a handover procedure, e.g. using a MOB_BSHO_REQ (BS-initiated HO request) message. The S-BS forwards HO requests from MSl and MS2 to the T-BS. It is to be noted that there may be more than one T-BS.

The T-BS responds to the handover requests.

When the T-BS response arrives, the S-BS may select the mobile stations with lowest target CINR (or lowest target RSSI) for HO reject even if the T-BS indicated accept for that particular mobile stations.

As shown in Fig. 4, the MSl would consume much more radio network resources at the T-BS due to the MCS to be used at the T-BS compared with the MCS used at the S-BS. Therefore, a HO request from the MSl from the S-BS to the T-BS may be rejected by the S-BS.

According to an embodiment of the invention, a base station may minimize an overall network resource consumption due to load balancing between base stations by unicasting the adapted HO triggers to a selected subset of mobile stations .

In other words, adapted handover parameters may be transmitted to at least one specific mobile station. Referring to Fig. 1, this may be performed by the transceiver 130a. A mobile station may be selected as the at least one specific mobile station based on a radio network resource consumption of the mobile station. This may be performed by the processor 110a shown in Fig. 1.

For example, for fine changes in load, the base station may send MS-specific MS_NBR-ADV (Mobile Station Neighbor Advertisement) unicast on primary management CID (Connection ID) to selected mobile stations with worst link and best neighbor performance. It is to be noted that other criteria for selecting the mobile stations may be used.

According to an embodiment of the invention, fine adjustment of base station load may be carried out by varying advertised HO trigger values in time. In other words, the adapted handover parameters may be varied over time. This may be performed by the processor 110a shown in Fig. 1.

Fig. 5 shows time charts illustrating an example of time- varying changes of advertised HO trigger values. The upper time chart shows transition of an original state to a new state of the advertised HO trigger values. The original and new states may represent advertised HO trigger values for different evaluated loads of the base station.

For example, for fine changes in load, the base station may vary the advertised HO trigger values over time as shown in the lower flow chart in Fig. 5. The intervals between the original state and the new state may be adjustable. Mobile stations may act upon the received HO trigger values and load of the base station can be lowered.

According to an embodiment of the present invention, load balancing between base stations can be achieved, which is transparent to mobile stations. Moreover, overall network consumption can be reduced.

According to an aspect of the invention, an apparatus of a communications network comprises processing means for evaluating a load of the apparatus, and adapting handover parameters to be advertized for mobile station decided handover in case the evaluated load has reached a predetermined limit. The apparatus may comprise the apparatus 100a shown in Fig. 1 and the processing means may comprise the processor 110a.

The apparatus may further comprise interfacing means for exchanging radio resource management information between the apparatus and at least one neighboring apparatus in the communications network. The at least one neighboring apparatus may be the apparatus 100b. The interfacing means may comprise the interface 120a. The processing means may evaluate a load of the at least one neighboring apparatus from the exchanged radio resource management information, and adapt the handover parameters to be advertized in case the evaluated load of the apparatus and the evaluated load of the at least one neighboring apparatus have reached predetermined limits.

The processing means may determine a load distribution between the apparatus and the at least one neighboring apparatus from the radio resource management information, wherein the determined load distribution indicates the predetermined limit for the apparatus and the predetermined limit for the at least one neighboring apparatus.

The processing means may adapt the handover parameters to be advertized in accordance with a function of the evaluated load of the apparatus and the load of the at least one neighboring apparatus. The function may induce handover to at least one specific apparatus of the at least one neighboring apparatus.

The apparatus may further comprise transmitting means for transmitting the adapted handover parameters. The transmitting means may comprise the transceiver 130a. The processing means may estimate an overall radio network resource consumption resulting from accepted handover requests which are based on the transmitted adapted handover parameters, and reject at least one of the accepted handover requests based on the estimated overall radio network resource consumption .

Alternatively or in addition, the transmitting means may transmit the adapted handover parameters to at least one specific mobile station, and the processing means may select a mobile station as the at least one specific mobile station based on a radio network resource consumption of the mobile station.

The processing means may vary the adapted handover parameters over time.

It is to be understood that the above description of embodiments of the invention is illustrative of the invention and is not to be construed as limiting the invention. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims .

Claims

CLAIMS :

1. An apparatus of a communications network, the apparatus comprising: a processor configured to evaluate a load of the apparatus, and adapt handover parameters to be advertized for mobile station decided handover in case the evaluated load has reached a predetermined limit.

2. The apparatus of claim 1, further comprising an interface configured to exchange radio resource management information between the apparatus and at least one neighboring apparatus in the communications network, wherein the processor is configured to evaluate a load of the at least one neighboring apparatus from the exchanged radio resource management information, and adapt the handover parameters to be advertized in case the evaluated load of the apparatus and the evaluated load of the at least one neighboring apparatus have reached predetermined limits .

3. The apparatus of claim 2, wherein the processor is configured to determine a load distribution between the apparatus and the at least one neighboring apparatus from the radio resource management information, wherein the determined load distribution indicates the predetermined limit for the apparatus and the predetermined limit for the at least one neighboring apparatus.

4. The apparatus of claim 2 or 3, wherein the processor is configured to adapt the handover parameters to be advertized in accordance with a function of the evaluated load of the apparatus and the load of the at least one neighboring apparatus .

5. The apparatus of claim 4, wherein the function is configured to induce handover to at least one specific apparatus of the at least one neighboring apparatus.

6. The apparatus of any one of claims 1 to 5, comprising a transmitter configured to transmit the adapted handover parameters, wherein the processor is configured to estimate an overall radio network resource consumption resulting from accepted handover requests which are based on the transmitted adapted handover parameters, and reject at least one of the accepted handover requests based on the estimated overall radio network resource consumption.

7. The apparatus of any one of claims 1 to 6, comprising a transmitter configured to transmit the adapted handover parameters to at least one specific mobile station, wherein the processor is configured to select a mobile station as the at least one specific mobile station based on a radio network resource consumption of the mobile station .

8. The apparatus according to any one of claims 1 to 7, wherein the processor is configured to vary the adapted handover parameters over time.

9. A method comprising: evaluating a load of an apparatus of a communications network; and adapting handover parameters to be advertized for mobile station decided handover in case the evaluated load has reached a predetermined limit.

10. The method of claim 9, further comprising: exchanging radio resource management information between the apparatus and at least one neighboring apparatus in the communications network; evaluating a load of the at least one neighboring apparatus from the exchanged radio resource management information; and adapting the handover parameters to be advertized in case the evaluated load of the apparatus and the evaluated load of the at least one neighboring apparatus have reached predetermined limits.

11. The method of claim 10, comprising: determining a load distribution between the apparatus and the at least one neighboring apparatus from the radio resource management information, wherein the determined load distribution indicates the predetermined limit for the apparatus and the predetermined limit for the at least one neighboring apparatus.

12. The method of claim 10 or 11, comprising: adapting the handover parameters to be advertized in accordance with a function of the evaluated load of the apparatus and the load of the at least one neighboring apparatus .

13. The method of claim 12, wherein the function is configured to induce handover to at least one specific apparatus of the at least one neighboring apparatus.

14. The method of any one of claims 9 to 13, comprising: transmitting the adapted handover parameters; estimating an overall radio network resource consumption resulting from accepted handover requests which are based on the transmitted adapted handover parameters; and rejecting at least one of the accepted handover requests based on the estimated overall radio network resource consumption.

15. The method of any one of claims 9 to 14, comprising: transmitting the adapted handover parameters to at least one specific mobile station, wherein a mobile station is selected as the at least one specific mobile station based on a radio network resource consumption of the mobile station.

16. The method according to any one of claims 9 to 15, comprising: varying the adapted handover parameters over time.

17. A computer program product including a program for a processing device, comprising software code portions for performing the steps of any one of claims 9 to 16 when the program is run on the processing device.

18. The computer program product according to claim 17, wherein the computer program product comprises a computer- readable medium on which the software code portions are stored.

19. The computer program product according to claim 17, wherein the program is directly loadable into an internal memory of the processing device.