WO2012055445A1

WO2012055445A1 - Method and apparatus for determining network coverage

Info

Publication number: WO2012055445A1
Application number: PCT/EP2010/066506
Authority: WO
Inventors: Attila Bader
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2010-10-29
Filing date: 2010-10-29
Publication date: 2012-05-03

Abstract

A method of monitoring radio coverage of a first communications network in the area served by a second communications network is disclosed. The method comprises instructing (102) a controller node of the second network to send to mobile terminals operating in the second network a message specifying a radio channel of the first network and instructing the mobile terminals to measure at least one radio parameter of the radio channel, and to report results of the measurement together with location of the mobile terminals. The method further includes receiving (104) in the first communications network results of the measurement from the controller node and mapping (110) the results of the measurement to determine areas where the radio parameter of the radio channel of the first communications network is not within required limits or where the radio channel of the first communications network is not received. Corresponding network node and mobile terminal are also disclosed.

Description

Method And Apparatus For Determining Network Coverage

Technical Field

The present invention relates to wireless communications networks, in general, and in particular to measurement of network coverage of a newly deployed network overlapping an existing network.

Background

Mobile wireless communications networks exist for over 20 years now and they evolve to provide more services and more bandwidth to the users. Each time a new network is deployed or when an existing one is expanded network operators carefully plan location of base stations in order to optimise the number of base stations and radio coverage they provide. It is in the interest of the operator to limit the number of base station and to maintain good radio coverage ensuring good delivery of services. The process of planning the network (or specifically planning location of the base station) can be to a large extent an automated exercise in which specialised software is used. The software uses maps to understand topography of the area where the network is going to be deployed. Because the network is required where the subscribers are, i.e. in urban areas, there is a problem with buildings that modify and potentially block radio signals. Although the buildings are taken into account when the location of the base station is planned the theoretical exercise is not always exactly replicated in real life.

In order to verify actual network coverage operators use so called drive tests where a specialised receivers for monitoring are installed in cars driving streets of a town or city to measure radio signals of the newly deployed network. Cars can move on the streets and measure the radio signal on the streets. Most of the subscribers are on the pavements, in buildings, parks, etc. These places are not accessible for cars. Similar tests can be performed by people carrying similar specialised receivers that measure the radio signals. Although these people can access more locations than cars, they still can not freely access all locations where real life subscribers are. Additionally, the number of cars for drive tests, number of people carrying the specialised equipment and time that can be allocated for such tests are limited, which means that such tests of network coverage are expensive and still have the drawback of not covering some locations where in normal use of the network the subscribers are located.

Summary

It is the object of the present invention to obviate at least some of the above disadvantages and provide an improved method, network management node and mobile terminal for monitoring radio coverage of a communications network.

Accordingly, the invention seeks to preferably mitigate, alleviate or eliminate one or more of the disadvantages mentioned above singly or in any combination.

According to a first aspect of the present invention there is provided a method of monitoring radio coverage of a first communications network in the area served by a second communications network. The method comprising instructing a controller node of the second communications network to send to mobile terminals operating in the second communications network a message specifying a radio channel of the first communications network. The message instructs the mobile terminals to measure at least one radio parameter of the radio channel and to report results of the measurement together with location of the mobile terminals at the time of the measurement. The method further comprises receiving in the first communications network results of the measurement from the controller node and then mapping the results of the measurement to determine areas where the radio parameter of the radio channel of the first communications network is not within required limits.

According to a second aspect of the present invention there is provided a network management node comprising a radio network optimisation function. The radio network optimisation function, in turn, comprises a second interface for communication with nodes of a second communications network. The radio network optimisation function is adapted to instruct a controller node of the second communications network to send to mobile terminals operating in the second communications network a message specifying a radio channel of the first communications network and instructing the mobile terminals to measure at least one radio parameter of the radio channel. The message also instructs the mobile terminals to report results of the measurement together with location of the mobile terminals at the time of the measurement. The second interface is adapted to receive results of the measurement from the controller node. The radio network optimisation function is adapted to map the results of the measurement to determine areas where the radio parameter of the radio channel of the first communications network is not within required limits.

According to a third aspect of the present invention there is provided a mobile terminal adapted to operate in a second communications network. The mobile terminal comprises a first monitoring module for measuring at least one radio parameter of a first communications network and a location module adapted to determine location of the mobile terminal. The mobile terminal is adapted to receive a message specifying a radio channel of the first communications network and instructing the mobile terminal to measure the at least one radio parameter of the radio channel and to report results of the measurement together with location of the mobile terminal at the time of the

measurement. The first monitoring module is adapted to measure the at least one radio parameter in response to the message, wherein the mobile terminal is adapted to send results of the measurement to the second communications network. According to a fourth aspect of the present invention there is provided a radio network optimisation function for use in a wireless communications network. The radio network optimisation function comprises a second interface for communication with nodes of a second communications network. The radio network optimisation function is adapted to instruct a controller node of the second communications network to send to mobile terminals operating in the second communications network a message specifying a radio channel of the first communications network and instructing the mobile terminals to measure at least one radio parameter of the radio channel. The message also instructs the mobile terminals to report results of the measurement together with location of the mobile terminals at the time of the measurement. The second interface is adapted to receive results of the measurement from the controller node. The radio network optimisation function is adapted to map the results of the measurement to determine areas where the radio parameter of the radio channel of the first communications network is not within required limits.

Further features of the present invention are as claimed in the dependent claims.

Brief description of the drawings

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

FIG. 1 is a diagram illustrating a method of monitoring radio coverage of a communications network in one embodiment of the present invention; FIG. 2 and 2A are diagrams illustrating a network management node for use in a wireless communications network in two alternative embodiments of the present invention; FIG. 3 and 4 illustrate a mobile terminal in two embodiments of the present invention;

FIG. 5 illustrates operation of a network management node in one embodiment of the present invention;

Fig. 6 illustrates modules of a radio network optimisation function for use in embodiments of the present invention.

Detailed description

To illustrate embodiments of the present invention a mature GSM

communications network and a newly deployed Long Term Evolution communications network are considered as illustrated in Fig. 5. The invention is also applicable to other combinations of communications networks deployed in different technologies, e.g mature 3G network and the new LTE network, etc.

With reference to Fig. 1 embodiments of a method of monitoring radio coverage of the LTE network (first network) in the area served by the GSM network (second network) are discussed.

A size of a LTE cell is small compared to a size of a GSM cell and therefore it is required to deploy more LTE base stations (also known as eNodeBs) in order to cover the area of the GSM cell. In consequence it is important to keep the number of deployed eNodeBs small by determining correct positions for their location. To verify if the determined positions provide coverage of the LTE network as expected the method comprises a radio network optimisation function (RNO) 202 of an OSS node (operation and support system) illustrated in Fig. 2 instructing 102 a base station controller node of the GSM communications network to initiate measurements of at least one radio parameter of a radio channel of the LTE network. In a preferred embodiment the radio channel to be measured is a broadcast channel because each mobile terminal can listen to it. Specifically a Broadcast Control Channel (BCCH) is a good candidate for the measurement. The advantage of measuring BCCH channel is that it is always on and transmits at constant power. However, in alternative embodiments it could be a traffic channel or other control channel, as well as a reference signal. It is possible to measure the signal strength of a traffic channel without decoding it, for example by measuring the carrier frequency and ignoring the modulation. When the second network is a GSM network then the BSC initiates

measurements of at least one radio parameter. However, the invention might be applied when the second network is other than GSM, e.g. WCDMA, TDSCDMA, LTE or other future radio network. In case of WCDMA a Radio Network Controller (RNC) performs this function, whereas in LTE the control function is implemented in the base station (eNodeB).

The RNO 202 of the OSS node instructs the base station controller 504 to send to mobile terminals operating in the GSM network a message which identifies the broadcast channel of the first communications network that should be measured. The broadcast channels in one embodiment is identified by a frequency or in another embodiment by a code used to decode said broadcast channel or in any other way known to a person skilled in the art. The message also instructs the mobile terminals to measure the at least one radio parameter of the broadcast channel of the LTE network 502. The at least one radio parameter may be for example a signal strength, other examples of parameters that are measured in various embodiments of this invention include code power, signal to noise ratio, received signal quality and related parameters. The message also instructs the mobile terminal to report results of the measurement to the base station controller 504. The measurement results are sent by the base station controller 504 to the OSS 200 in real time in one embodiment or periodically in files in an alternative embodiment. Preferably the results are reported together with location of the mobile terminals at the time of the measurement. To ensure good correlation of the measurements in a preferred embodiment the measurements include time-stamps. When the results are received 104 in the OSS 200 the R O 202 maps 110 the results and determine areas where the measured radio parameter of the first communications network does not meet defined requirements (i.e. is not within required limits). The mapping also allows identifying regions where the broadcast channel of the LTE network is not received at all. Preferably the results received by the RNO 202 include measurements of at least one radio parameter of the second communications network to correlate the results of measurements for both communications networks in order to determine areas with poor coverage and/or poor service quality. In this way embodiments of the invention when applied to a LTE network overlapping a GSM network allow for combining LTE throughput measurements in correlation with GSM radio measurements, which can be used for identifying the LTE coverage holes and scarce radio environment that negatively influence the user level performance.

In a preferred embodiment a total throughput of a cell and the performance of the LTE system are measured by LTE base stations or by external performance management functions. Therefore the measurement results received by the OSS 200 from the base station controller node 504 are correlated 106 with the LTE network throughput measured by base stations of the LTE network. In alternative embodiments a parameter known as cell load is measured and used by the OSS 200 instead of the total throughput of a cell. The cell load is a function of the total throughput and the number of active users and depends on the number of users the throughput is distributed.

Also preferably, the measurement results received by the OSS 200 from the base station controller node 504 are correlated 108 with throughput received by individual mobile terminals operating in the LTE network. The throughput received by the individual mobile terminal in a given cell is measured by a LTE base station serving this cell and is a measure of end-to-end performance. The total throughput and the throughput for each user are measured in the LTE base stations (eNodeBs). These measurements are implemented in the eNodeB, but in alternative embodiments it can be measured by using external traffic probes/tools. The total cell throughput measured by a base station of the LTE network is received by the RNO function 202 or 202A via the first interface 206. In consequence, advantageously the LTE cells' throughput and performance measurements are combined with radio measurements done by the GSM system. The results are then combined with the geographic position of the mobile terminals that took the measurements and represented on a map. The position of the mobile terminals that take the measurements can be determined either by GPS or by any position

determination method provided by the radio system. In a more accurate solution positions of the mobile terminals are determined using GPS coordinates (accuracy is few meters) to correlate the positions of the mobile terminals with the radio

measurements. This can be done by measuring and reporting the GPS coordinates by the mobile terminals. Alternatively position determination function provided by the GSM system can be used, e.g. time based or signal strength based triangulation method (accuracy 50-100 m).

In the map the LTE coverage, the total throughput of the cell and the end-to-end user performance are displayed. The spots where there is no LTE coverage or there is poor radio signal are indicated. This can be used in deciding on how to extend the LTE network with new cells (i.e. deploying new base stations), but also gives an overview of the quality of the service and radio environment provided by the existing LTE cells. The LTE coverage maps are compared with the total throughput. The signal strength measured by the GSM system is compared with the user throughput and the total throughput measured in the LTE cells. Low throughput combined with low signal strength indicates spots where the LTE radio environment should be improved. New LTE cells are proposed in areas where there is no coverage or the radio coverage is pure, which means that signal level, or code power is below a limit. (The system has some adaptive behaviour, ie it increases the transmit power in order to compensate the low signal level, so if transmitted power is above a limit it also indicates low coverage. It is correct to say in general that radio parameters are out of a range.) New cells are also proposed where the throughput is high. Cells where there is good coverage but pure end-to-end performance are also indicated. The radio environment and throughput measurements are stored in a database. In this way historical data will be available and trends can be analysed.

In an alternative embodiment in response to the received results of the measurements the method includes the OSS 200 instructing 112 a base station of the LTE network to change a parameter of radio transmission used by the base station. When the measurements show that the radio signal of the LTE network is weak in a certain area, the OSS 200 instead of recommending deployment of a new base station sends an instruction to increase transmit power in a sector served by the base station (or even more than one sector and/or more than one base station). In this way better signal is provided in this area if there is an available margin in the base station. If the transmit power increase does not improve the LTE network coverage to a level that satisfies the LTE network operator then after a second round of measurements deployment of a new base station can be recommended. Increasing the transmit power is just one example that can be used to improve coverage of the LTE network. Other examples of parameters or operations that can be adjusted in response to received measurement results, in order to improve network coverage in certain areas, include frequency allocation, frequency hopping and other transmission parameter of LTE could be adjusted based on GSM radio measurements. As explained above, the proposed solution uses the existing GSM infrastructure (or infrastructure of other mature network) to measure LTE radio environment. This can be used also at the initial deployment phase of LTE. It can be used to expand the network where it is mostly needed. Clearly, the advantage of this solution is its low cost which is due to using the existing infrastructure and not using time consuming drive tests. The large number of GSM mobile terminals that perform the measurements in places not accessible during drive tests provide additional advantage of greatly improved spatial accuracy. In one embodiment the mobile terminals are instructed to measure more than one radio parameter of the broadcast channel of the LTE network. In this way the R O function 202 receives even more accurate information about LTE network coverage. The RNO function 202 correlates the available measurements and presents them on a map. The increase number of measured parameters allows for determining relationship between them and fine tuning transmit parameters of the LTE base stations in order to improve LTE coverage (e.g. the mentioned above frequency allocation, frequency hopping and other transmission parameter of LTE).

A network management node providing functions of an Operation Support System, OSS, 200 for both the GSM and LTE networks will now be described with reference to Fig. 2, 2A and Fig. 5. The network management node 200 comprises a radio network optimisation function, RNO, 202, which, in turn, comprises a second interface 204 for communication with the GSM network 500. In a preferred

embodiment the RNO 202 also comprises a first interface 206 for communication with nodes of the LTE network 502. It is possible, however, that in alternative embodiments the OSS 200 comprises another RNO function 202A dedicated to optimizing LTE radio environment as illustrated in Fig. 2A. In this embodiment the first interface 206 for communication with nodes of the LTE network 502 is implemented in this dedicated LTE RNO function 202A. The two RNO functions 202A and 202B are in

communication.

The RNO 202 has several functions used for optimizing the GSM radio environment. These functions use the radio recording functions implemented in the GSM system. In the GSM network a Broadcast Control Channel (BCCH) Frequency Allocation Recordings (BAR) is used to measure the radio parameters of the broadcast control channels. BCCH is always active in the GSM system, so it is possible to measure the radio parameters of the BCCH at any time. Mobile terminals are able to measure several BCCH frequencies. A corresponding RNO GSM function 202 or 202B activates the BAR in the GSM system for a predefined cell set. The BCCH frequencies that should be measured by the mobiles are specified in this operation. When the recording is started the BSC activates the corresponding radio measurements in the GSM mobile terminals. The mobile terminals measure the signal strength of the specified frequencies periodically. The average of the signal strength is reported to the BSC 504.

The RNO function 202 is adapted to instruct the BSC 504 of the of the GSM network 500 to send to GSM mobile terminals a message specifying a broadcast channel of the LTE network 502 instead or in addition to specifying broadcast channel of the GSM network. The message instructs the GSM mobile terminals to measure at least one radio parameter of the LTE broadcast channel and to report the results of the measurement together with location of the mobile terminals at the time of the measurement to the BSC 504. In this way, in order to obtain information of the LTE network radio coverage, the LTE broadcast frequencies are added to the list of frequencies monitored by the GSM mobile terminals. When the LTE cell signal is strong enough, the average signal strength of the LTE cells is included in the reported results and in this way they are sent to the BSC 504. The RNO 202 receives the results of the measurements via the second interface 204 from the BSC 504. In this way the radio measurements for all reported LTE cells are collected and the LTE radio coverage and radio environment will be available for the GSM cells. The RNO function 202 performs mapping of the results of the measurement to determine areas where the radio parameter of the broadcast channel of the LTE network 502 is not within required limits or where the broadcast channel of the first communications network 502 is not received at all. Preferably, the results are displayed as a density map with the granularity of the GSM cells, which is a few hundred meters in urban areas.

With reference to Fig. 6 modules of the RNO function 202 will now be described. A data correlation module 600 receives radio measurement data 602 (e.g. signal strength of BCCH of the LTE network 502) and positioning data 604 of the GSM mobile terminals. This information is received from the base station controller 504 of the GSM network 500. The data correlation module 600 also receives LTE performance data 606 (e.g. cell throughput) from the LTE network 502. The data correlation module 600 performs special correlation of the collected data and represents the results on a map 612 to indicate areas where the LTE network coverage and/or performance is not as required. The results of the data correlation are also stored in a database 608, which in one embodiment is integrated with the RNO function 202 and in alternative embodiment is an external module in communication with the RNO function. With results of correlation obtained at different times it is possible to analyse trends 610 in

LTE network coverage and/or performance. These trends may be caused by maturing of the LTE network resulting in more LTE base stations being deployed, but also increased number of LTE mobile terminals that operating in the network that obviously will have effect on cells throughput. These trends can also be illustrated on the map 612.

Fig. 3 and Fig. 4 illustrate two embodiments of a GSM mobile terminal 300 comprising a first monitoring module 304 for measuring at least one radio parameter of the LTE network 502 and a location module 308 (e.g. GSM module) adapted to determine location of the mobile terminal 300. The mobile terminal is adapted to receive, via transmitter/receiver module 310, a message specifying a broadcast channel of the LTE network 502. The message also instructs the mobile terminal 300 to measure the at least one radio parameter (e.g. signal strength) of the LTE broadcast channel (e.g. BCCH) and to report results of the measurement together with location of the mobile terminal 300 at the time of the measurement to a GSM base station to which the mobile terminal is connected. The first monitoring module 304 measures the signal strength of the BCCH of the LTE network in response to the message. Once the measurement is done, or in alternative embodiment in real time or near real time, the mobile terminal 300 sends results of the measurement to the BSC504 via a GSM base station. The mobile terminal comprises a second monitoring module 306 for measuring at least one radio parameter of the GSM network 500.

In one embodiment of the mobile terminal 300 (illustrated in Fig. 3) the first and second monitoring modules 304, 306 are implemented as software modules in a processor 302 of the mobile terminal. In an alternative embodiment (illustrated in Fig. 4) the first and second monitoring modules 304, 306 are implemented as individual modules (preferably hardware) connected to the processor 302 of the mobile terminal.

Claims

1. A method of monitoring radio coverage of a first communications network in the area served by a second communications network comprising:

- instructing (102) a controller node of the second communications network to send to mobile terminals operating in the second communications network a message specifying a radio channel of the first communications network, the message instructing the mobile terminals to measure at least one radio parameter of the radio channel and to report results of the measurement together with location of the mobile terminals at the time of the measurement;

- receiving (104) in the first communications network results of the measurement from the controller node;

- mapping (110) the results of the measurement to determine areas where the radio parameter of the radio channel of the first communications network is not within required limits.

2. The method according to claim 1, wherein the results received include

measurements of at least one radio parameter of the second communications network to correlate the results of measurements for both communications networks in order to determine areas with poor coverage and/or poor service quality.

3. The method according to claim 1 or claim 2 comprising correlating (106) the measurement results received from the controller node of the second communications network with a throughput of cells of the first communications network measured by base stations of the first communications network.

4. The method according to any one of claims 1 - 3 comprising correlating (108) the measurement results received from the controller node of the second communications network with throughput received by individual mobile terminals operating in the first communications network measured by a base station of the first communications network.

5. The method according to any one of preceding claims further comprising instructing (112) a base station of the first communications network to change a parameter of radio transmission used by the base station in response to the received results of the measurements.

6. The method according to any one of preceding claims, wherein the radio channel is a broadcast channel.

7. A network management node (200) comprising a radio network optimisation function (202), wherein the radio network optimisation function comprises a second interface (204) for communication with nodes of a second communications network (500), wherein the radio network optimisation function (202) is adapted to instruct a controller node (504) of the second communications network (500) to send to mobile terminals operating in the second communications network (500) a message specifying a radio channel of the first communications network (502), the message instructing the mobile terminals to measure at least one radio parameter of the radio channel and to report results of the measurement together with location of the mobile terminals at the time of the measurement, the second interface (204) being adapted to receive results of the

measurement from the controller node (504) and the radio network optimisation function (202) being adapted to map the results of the measurement to determine areas where the radio parameter of the radio channel of the first communications network (502) is not within required limits.

8. The node (200) according to claim 7, wherein the radio network optimisation function (202) comprises a first interface (206) for communication with nodes of the first communications network (502) and receiving cell throughput measured by a base station of the first communications network (502) and the radio network optimisation function (202, 202A) is adapted to correlate the measurement results received from the controller node (504) of the second communications network (500) with the cell throughput.

9. The node (200) according to claim 7 or claim 8 comprising a first interface (206) for communication with nodes of a first communications network (502) and receiving throughput received by individual mobile terminals operating in the first communications network (502) measured by a base station of the first communications network (502), wherein the radio network optimisation function (202) being adapted to correlate the measurement results received from the controller node (504) of the second

communications network (500) with the throughput received by individual mobile terminals operating in the first communications network (502).

10. The node (200) according to any one of claims 7 - 9 wherein the radio network optimisation function (202) is adapted to instruct a base station of the first communications network (502) to change a parameter of radio transmission used by the base station in response to the received results of the measurements.

11. The node (200) according to any one of claims 7 - 10, wherein the radio channel is a broadcast channel.

12. A mobile terminal (300) adapted to operate in a second communications network (500), the mobile terminal comprising a first monitoring module (304) for measuring at least one radio parameter of a first communications network (502) and a location module (308) adapted to determine location of the mobile terminal (300), the mobile terminal being adapted to receive a message specifying a radio channel of the first communications network (502) and instructing the mobile terminal (300) to measure the at least one radio parameter of the radio channel and to report results of the measurement together with location of the mobile terminal (300) at the time of the measurement and the first monitoring module (304) is adapted to measure the at least one radio parameter in response to the message, wherein the mobile terminal (300) is adapted to send results of the measurement to the second communications network (500).

13. The mobile terminal (300) according to claim 12 comprising a second monitoring module (306) for measuring at least one radio parameter of the second communications network (500) and the first and second monitoring modules (304, 306) are implemented as software modules in a processor of the mobile terminal.

14. The mobile terminal (300) according to claim 12 comprising a second monitoring module (306) for measuring at least one radio parameter of the second communications network (500) and the first and second monitoring modules (304, 306) are implemented as individual modules connected to a processor of the mobile terminal.

15. The mobile terminal (300) according to any one of claims 12 - 14 wherein the radio channel is a broadcast channel.

16. A radio network optimisation function (202) for use in wireless communications network, the radio network optimisation function (202) comprising a second interface (204) for communication with nodes of a second communications network (500), wherein the radio network optimisation function (202) is adapted to instruct a controller node (504) of the second communications network (500) to send to mobile terminals operating in the second communications network (500) a message specifying a radio channel of the first communications network (502), the message instructing the mobile terminals to measure at least one radio parameter of the radio channel and to report results of the measurement together with location of the mobile terminals at the time of the measurement, the second interface (204) being adapted to receive results of the measurement from the controller node (504) and the radio network optimisation function (202) being adapted to map the results of the measurement to determine areas where the radio parameter of the radio channel of the first communications network (502) is not within required limits.