Method for simulating operating conditions of a mobile telecommunication network

0001The present invention concerns a method for simulating operating conditions of a mobile telecommunication network.

0002Simulation methods are known for optimising, before actual physical implementation of a mobile telecommunication system, a deployment of radio base stations included in said system and a design of a decision-making network infrastructure which is intended to manage said network, in order to define a system able to provide optimal communication service at the lowest possible cost.

0003Such a known simulation method is described in the patent document EP-A-1 317 158. The method consists in making a plurality of snapshots or configuration states of the network correlated one in respect to the following one by means of at least one correlating parameter. At each step of the method, a snapshot thus linked to the previous one is used. The connectivity of the mobile terminals is first calculated based on simulated pilot signals emitted by the base stations of the network and as received by the mobile terminals. Then, transmission powers in the uplink and the downlink for each connection are determined based on a coupling loss term that respectively counts for the average attenuation of the transmitted signals between the antenna connector of a mobile terminal and the antenna connector of a base station and conversely. The quality of service or grade of service of each connection between a mobile terminal and a base station can then be determined.

0004We recall that the coupling loss between a base station and a mobile terminal counts for four items : the antenna gain of the base station, the propagation loss over the transmission channel between the base station and the mobile terminal, the antenna gain of the mobile terminal as well as the body loss that counts for the loss involved in the body, generally the head, of the user that handles the mobile terminal.

0005A crucial point in a simulation method is to accurately assess the coupling loss term in order for an operator to properly design a mobile telecommunication network in term of coverage (the number of base stations needed to cover a zone) and in term of capacity (the number of mobile terminals that a network can simultaneously handle). This is due to the fact that the coupling loss term between a mobile terminal and a base station affects how the base station covers its proper cell and how it interferes with the neighbouring cells of the network. Interferences between cells have an important role in mobile telecommunication networks and particularly in CDMA networks.

0006The assessment of the coupling loss implies the assessment of all its components. Nowadays, assessments of the antenna gain of a base station and the propagation loss over the channel between the base station and the mobile terminal are very sophisticated and accurate operations. This is not unfortunately the case for the gain of the antenna of a mobile terminal and for the body loss.

0007Generally, for these two latter items, the assessments are done by means of simplistic models, i.e. for example by considering an omnidirectional radiating diagram for the antenna of the mobile terminal and by introducing correcting factors for the mean directional resulting gain as well as for the body loss.

0008Nevertheless, this approach is not correct due to the fact that the gain of an antenna of recent mobile terminals for which the trend is towards minimizing the emission in the direction of the user varies in a great measure with the directions. Actually, the mean directional gain is theoretically equal to 1 all over 4π steradians while the gain of an antenna can vary from -30 dB for the antenna poles to 2 dB or more in privileged directions. Thus, if signals are received by the antenna in a direction corresponding to a minimum of the gain, they can be strongly attenuated. A model of a mean gain constant all over the direction cannot take this situation into account and thus is not correct.

0009This approach is not correct also due to the body loss that also introduces a directional effect on the coupling loss.

0010Furthermore, the coupling loss can considerably vary with the usage that is made of a mobile terminal. For example, a mobile terminal is not in the same relationship with a base station if it is used either as a phone close to user's head near an ear or as a video terminal in the hands in front of the user's body. A model that don't take into account such situations is thus not correct.

0011The aim of the method of the present invention is to overcome the problem above raised.

0012For this purpose, the present invention concerns a method for simulating operating conditions of a mobile telecommunication network comprising a plurality of base stations and a plurality of mobile terminals, each mobile terminal being handled by a user and forming with said user what is called a mobile unit, said method including at least one step for determining the coupling loss function value between each said base station and each said mobile terminal. The method of the invention is characterized in that a step for determining the coupling loss function value includes a step for determining the value of a function, called mobile unit loss function, representative of the losses that are defined in relation with a coordinates system linked to each mobile unit, and in that said method includes a step for orientating the coordinates system linked to each mobile unit based on the displacement of said mobile unit.

0013According to another advantageous characteristic of the invention, the step of orientating the coordinates system of the mobile unit loss function is based on the simulated use of the considered mobile terminal.

0014According to another advantageous characteristic of the invention, the coordinates system is a polar coordinate system defined by a directional vector representative of the origin axis of the mobile unit loss function and by at least one angle of incidence.

0015According to another advantageous characteristic of the invention, the displacement of a mobile unit is represented by the speed vector of said mobile unit.

0016According to another advantageous characteristic of the invention, the step of orientating the coordinates system which the mobile unit loss is linked to includes a step of defining a relationship between said directional vector linked to a mobile unit and the speed vector thereof.

0017According to another advantageous characteristic of the invention, the mobile unit loss function includes the antenna diagram function of the mobile terminal of said mobile unit.

0018In a same way, the mobile unit loss function includes the body loss function of the user handling said mobile terminal of said mobile unit.

0019The characteristics of the present invention will emerge from a reading of the following description given in relation to the appended drawings, amongst which : <ul id="ul0001" list-style="none" compact="compact"><li>Fig. 1 depicts a mobile communication network for illustration of the method of the present invention,</li><li>Fig. 2 depicts the radiating diagram of a mobile terminal and,</li><li>Figs. 3a and 3b depict the way the relation between the directional vector of a mobile terminal and the speed vector is made according to two aspects of the present invention.</li></ul>

0020Fig. 1 depicts as an example a transmission network that comprises two base stations BS 1 and BS2 and a mobile terminal MT. A user US (only his head is shown) is using and handling the mobile terminal MT, the mobile terminal MT being against his right ear. During the communication of the user US, the base stations BS1 and BS2 send to the mobile terminal MT signals that are received by the antenna of the mobile MT and the mobile terminal MT sends signals to each of the base stations BS1 and BS2.

0021A simulation method generates snapshots that are representative of different configuration states of the network, generally given by the position of the mobile terminals relative to the base stations of the network, and simulates accordingly for each snapshot the levels of the signals that are received by each mobile terminal MT and those that are emitted by each mobile terminal towards the base stations. After a period of time and after having considered a plurality of snapshots, the simulation method enable the quality of service or grade of service that the network is able to present to be deduced. The entire simulation method can be considered as including a basic simulation function that is iteratively repeated for each snapshot and of which the result depends on the power levels as received by the base stations and by the mobile terminal.

0022If we consider only for clarity purposes, those power levels that are received by a mobile terminal MT from the two base stations of Fig. 1, one can write :<maths id="math0001"><math display="block"><mrow><msub><mrow><mtext>Basic simulation function for the mobile terminal MT = f (P</mtext></mrow><mrow><mtext>R</mtext></mrow></msub><msub><mrow><mtext>1, P</mtext></mrow><mrow><mtext>R</mtext></mrow></msub><mtext>2)</mtext></mrow></math><img file="EP1534032A1_D0001.tif" /></maths>    where P_R1 and P_R2 are the power levels as received by the mobile terminal MT respectively from the base stations BS1 and BS2. The power levels P_R1 and P_R2 as received by the mobile terminal MT depend on the power levels P_T1 and P_T2 as transmitted by the base stations BS1 and BS2 as well as on the coupling losses between the mobile terminal of each of the both base stations BS1 and BS2, so one can write :<maths id="math0002"><math display="block"><mrow><msub><mrow><mtext>Basic simulation function for the mobile terminal MT = f (P</mtext></mrow><mrow><mtext>T</mtext></mrow></msub><msub><mrow><mtext>1 x G</mtext></mrow><mrow><mtext>BS1</mtext></mrow></msub><msub><mrow><mtext>, P</mtext></mrow><mrow><mtext>T</mtext></mrow></msub><msub><mrow><mtext>2 x G</mtext></mrow><mrow><mtext>BS2</mtext></mrow></msub><mtext>)</mtext></mrow></math><img file="EP1534032A1_D0002.tif" /></maths>    wherein G_BS1 and G_BS2 are the coupling losses between the base stations BS1 and BS2 respectively and the mobile terminal MT.

0023The coupling loss can be expressed as follows :<maths id="math0003"><math display="block"><mrow><msub><mrow><mtext>G = A</mtext></mrow><mrow><mtext>BS</mtext></mrow></msub><msub><mrow><mtext> x PL x A</mtext></mrow><mrow><mtext>MT</mtext></mrow></msub><mtext> x Body loss</mtext></mrow></math><img file="EP1534032A1_D0003.tif" /></maths>    wherein A_BS is the antenna gain of the base station as considered, PL is the propagation loss between said base station and the mobile terminal, A_MT is the antenna gain of the mobile terminal and BL is the body loss.

0024In a simulation method, the two first terms A_BS and PL depend on the considered base station. They can be expressed as a quantity that notably varies with the direction θ of the beam as considered : K(θ) = A_BS(θ) x PL.

0025As above-mentioned, the coupling loss also includes the gain of the antenna of the mobile terminal MT and the body loss. The first term can be deduced from the radiating diagram of the antenna whereas the second term can be deduced from measurements made for specific usage of the mobile terminal. As it can be easily understood, they are linked to an entity that is constituted of the user US and its mobile terminal MT as they are in relation one to the other. This relationship mainly depends on the use of the mobile terminal. This entity is called thereafter the mobile unit MU. The combination of the first and second terms forms an attenuation diagram, which is called thereafter the mobile unit loss function and which is shown in Fig. 1 under the reference MUL.

0026The coupling loss can then be expressed as follows :<maths id="math0004"><math display="block"><mrow><msub><mrow><mtext>G</mtext></mrow><mrow><mtext>BS</mtext></mrow></msub><mtext>(θ) = K(θ) x MUL(θ).</mtext></mrow></math><img file="EP1534032A1_D0004.tif" /></maths>    where MUL(θ) is the mobile unit loss and thus can be written as A_MT x Body Loss.

0027The mobile unit loss MUL is linked to the mobile unit MU which means that it is known in a coordinates system that is linked to the mobile unit MU. The problem is that this coordinates system does not generally correspond to the coordinates system of the simulation process.

0028In the present description, note that the simulation process is made in a two-dimensional polar coordinates system that is defined by an axis xx' and an angle θ said the incidence angle. Nevertheless, it must be understood that the invention also applies in a three-dimensional coordinate system so that the polar coordinates can be expressed in terms of two angles θ and ϕ. In this case, the mobile unit loss diagram is also three-dimensional.

0029Let consider a coordinates system (a two-dimensional coordinates system only for simplicity purposes) that is linked to each mobile unit of the network (as defined just above) and that is used for the purpose of calculating the value taken by the mobile unit loss of the mobile terminal.

0030Fig. 2 shows a mobile unit MU as above defined and that is constituted of a mobile terminal MT and an user US in a particular relation one to the other. The coordinate system linked to the mobile unit MU is a two-dimensional polar coordinates system that is defined by an origin axis yy' and an angle α. For purpose of simplicity, the axis yy' is materialized by a vector, called the directional vector of the mobile unit MU and is referenced as to DV. The directional vector DV is linked to the mobile unit MU. Fig. 2 also shows the radiating diagram RD of the antenna of the mobile MT and the diagram BL of the body loss of the user in the particular relationship of the user and its mobile terminal MT in a considered usage. The resulting mobile unit loss diagram MUL which is a combination of the radiating diagram RD of the antenna of the mobile MT and the diagram BL of the body loss of the user is also shown.

0031When a beam B is incident with an angle of α in relation with the directional vector DV, the loss of the mobile unit is given in the coordinates system linked to the mobile unit MU by MUL(α), which results in the point <b>m</b> in the resulting diagram.

0032The directional vector DV of the mobile unit MU, as shown in Fig. 1, forms an angle β with the axis xx' of the coordinate system for the calculation of the simulation process. The coupling loss G(θ) can be thus deduced from the mobile unit loss MUL as determined in the coordinates system linked to the mobile unit MT by the following expression :<maths id="math0005"><math display="block"><mrow><mtext>G(θ) = K(θ) x MUL(θ + β)</mtext></mrow></math><img file="EP1534032A1_D0005.tif" /></maths>

0033As it can be understood, the angle β depends on the position and on the orientation of the mobile unit MU at the present moment, i.e. for the actual snapshot.

0034Note that the expression giving the result of the basic simulation function for the mobile terminal MT of Fig. 1 becomes the following :<maths id="math0006"><math display="block"><mrow><msub><mrow><mtext>Basic simulation function for the mobile terminal MT = f (P</mtext></mrow><mrow><mtext>T</mtext></mrow></msub><msub><mrow><mtext>1 x G</mtext></mrow><mrow><mtext>BS1</mtext></mrow></msub><msub><mrow><mtext>, P</mtext></mrow><mrow><mtext>T</mtext></mrow></msub><msub><mrow><mtext>2 x G</mtext></mrow><mrow><mtext>BS2</mtext></mrow></msub><mtext>)</mtext><mspace linebreak="newline" /><msub><mrow><mtext> = f (P</mtext></mrow><mrow><mtext>T</mtext></mrow></msub><msub><mrow><mtext>1 x G</mtext></mrow><mrow><mtext>BS1</mtext></mrow></msub><msub><mrow><mtext>(θ1), P</mtext></mrow><mrow><mtext>T</mtext></mrow></msub><msub><mrow><mtext>2 x G</mtext></mrow><mrow><mtext>BS2</mtext></mrow></msub><msub><mrow><mtext>(θ</mtext></mrow><mrow><mtext>2</mtext></mrow></msub><mtext>))</mtext><mspace linebreak="newline" /><msub><mrow><mtext> = f (P</mtext></mrow><mrow><mtext>T</mtext></mrow></msub><msub><mrow><mtext>1 x K</mtext></mrow><mrow><mtext>BS1</mtext></mrow></msub><msub><mrow><mtext>(θ</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><msub><mrow><mtext>) x MUL(θ</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><msub><mrow><mtext> + β), P</mtext></mrow><mrow><mtext>T</mtext></mrow></msub><msub><mrow><mtext>2 x K</mtext></mrow><mrow><mtext>BS2</mtext></mrow></msub><msub><mrow><mtext>(θ</mtext></mrow><mrow><mtext>2</mtext></mrow></msub><msub><mrow><mtext>) x MUL(θ</mtext></mrow><mrow><mtext>2</mtext></mrow></msub><mtext> + β))</mtext></mrow></math><img file="EP1534032A1_D0006.tif" /></maths>    where θ₁ and θ₂ are the incidence angle of the beam emitted by the base stations BS1 and BS2 and K_BS1(θ₁) and K_BS2(θ₂) are factors linked to the base stations BS1 and BS2 for the directions given by the angle θ₁ and θ₂.

0035In a simulation process, the displacement of the mobile terminal MT, and therefore the displacement of the mobile unit MU, is given at each snapshot.

0036According to the invention, a relationship is formed between the displacement of the mobile unit MU (and therefore the displacement of the mobile terminal MT) and the coordinates system linked to the mobile unit in order for that system to be oriented relative to the coordinates system of the simulation process.

0037Generally, the displacement of the mobile unit is represented by its speed vector V. The origin axis of the mobile unit loss diagram MUL is represented by the directional vector DV (as above mentioned). So, according to the invention, a relationship is formed between the speed vector V and the directional vector DV of the mobile unit MU. Therefore, as the speed vector V of the mobile unit MU is given, the directional vector DV of the mobile unit MU can be determined thanks to this relationship. The angle β can also be deduced and the mobile unit loss MUL(θ + β) for the considered beam can be obtained from the above expressions. The coupling loss G(θ) can be then calculated : G(θ) = K(θ) x MUL(θ + β).

0038According to an embodiment of the present invention, this relationship is only an angular relationship. For example, this expression can be under the form : the speed vector V and the directional vector form together an angle which value is τ (see Fig. 1). In this case, the angle β can be calculated by the following expression :<maths id="math0007"><math display="block"><mrow><mtext>β = {angle between V and xx'} - τ.</mtext></mrow></math><img file="EP1534032A1_D0007.tif" /></maths>

0039This relationship between the speed vector V and the directional vector DV depends on the usage of the mobile terminal at the considered time. For example, when using a vocal service, the mobile terminal MT is against the left (or the right) of the head of the user, slightly forwardly oriented. The directional vector will be then nearly perpendicular to the speed vector and slightly downwardly oriented whereas the speed vector is horizontal (see Fig. 1).

0040When using a video service, the mobile terminal MT is being in front of the eyes of the user and downwardly pointed. The directional vector will be then in the direction of the speed vector downwardly pointing (see Fig. 3a).

0041When using the mobile terminal as a camera, it is also in front of the user but now forwardly oriented. In this case, the directional vector is somewhat parallel to the speed vector (see Fig. 3b).

0042In the present description, for purpose of simplicity, the coordinates systems that are considered are two-dimensional systems and the polar coordinates are expressed in terms of an angle θ and a magnitude. One skilled in the art will understand that the coordinates systems can be three-dimensional coordinates systems so that the polar coordinates can then be expressed in terms of two angles θ and ϕ. In this case, the mobile unit loss diagram is also a three-dimensional diagram and two angles are to be considered between the directional reference axis xx' and the directional vector DV of the mobile unit.