Method for controlling the power for broadcasting a Cognitive Pilot Channel

The invention relates to a method for controlling the power for broadcasting a Cognitive Pilot Channel broadcasting lists of information to each of a plurality of meshes Mi (i=1 to n), n being the number of meshes in a geographical area comprising at least one base station (4) broadcasting the CPC to the meshes Mi. The method comprises the following steps: calculating for each mesh Mi a transmission power Pi; and broadcasting to each mesh Mi the Cognitive Pilot Channel with the power Pi.

TECHNICAL FIELD

The invention pertains to telecommunication field and concerns a method for controlling the power for broadcasting a Cognitive Pilot Channel transporting lists of information to a plurality of meshes Mi(i=1 to n), n being the number of meshes in a geographical area comprising at least one base station transmitting said CPC to said meshes Miwith a total transmission power P.

The invention also concerns a base station comprising means for broadcasting a Cognitive Pilot Channel to a plurality of meshes Mi(i=1 to n) with a total transmission power P, n being the number of meshes in a geographical area, said Cognitive Pilot Channel transporting lists of information to said meshes to allow a User Equipment located in a given mesh Mi(i=1 to n) to select an operator and/or a Radio Access Technology and/or a communication frequency available in said given mesh.

BACKGROUND ART

Cognitive Pilot Channel (CPC) is a concept used in cognitive radio to provide information to cognitive mobiles about the available operators, Radio Access Technologies (RAT) and Frequencies available in a geographical area.

Two Major concepts for Cognitive Pilot Channel are proposed by the E3 project and ETSI RRS Group: Mesh based and Optimised broadcast approach.In mesh based concept, a cell in a geographical area is divided into a plurality of meshes and information is provided about operators, RATs and Frequencies available in each mesh.In optimised broadcast concept, information about all the RATs and frequencies available in the cells is transmitted at once.

Although Mesh based concept is more precise than Optimised broadcast concept, it presents drawbacks resulting from the fact that the power used by the base station to broadcast said information is estimated to reach all mobiles. Thus no power control is used. The power is estimated at once to be sufficient for the users on the cell edge to be able to decode the broadcasted information.

Consequently, the same power is used for transmitting Cognitive Pilot Channel information to all meshes of the geographical area while the transmission of information to meshes close to the base station does not necessitate the same power as the transmission of said information to meshes situated on the outskirts of the geographical area. Thus a user equipment located in a peripheral mesh may not decode the information because of the power attenuation.

An object of the present invention is a method for optimizing the distribution of the transmission power in order to better control the power used to transmit the cognitive pilot channel (CPC) giving to a User Equipment the same probability of CPC content decoding in all the meshes.

Another object of the invention is a power control method that takes into account the attenuation du to the topography of each mesh in said geographical area.

SUMMARY OF INVENTION

Technical Problem

The invention is based on the fact that transmission of the Cognitive Pilot Channel content to meshes located near the base station requires less power than transmission of this content to meshes located at the periphery of the cell covered by the base station.

Thus, instead of transmitting the Cognitive Pilot Channel content with the same power to all the meshes of the geographical area, the power in the method according to the invention is distributed between said meshes to take into account the path loss that is likely to be seen by a user equipment in the geographical area.

Solution to Problem

This object is achieved by means of a method for controlling the power for broadcasting a Cognitive Pilot Channel (CPC) transporting lists of information to a plurality of meshes Mi(i=1 to n), n being the number of meshes in a geographical area comprising at least one base station adapted for transmitting said CPC to said meshes Miwith a total transmission power P.

The method according to the invention comprises the following steps:determining for each mesh Mi(i=1 to n) the distance dito said base station,calculating for each mesh Mi(i=1 to n) a transmission power Pias a function of said distance diand of said total transmission power P,broadcasting to each mesh Mi(i=1 to n) said Cognitive Pilot Channel with the power Pi.

Preferably, said power Piis inversely proportional to said distance di.

According to a preferred embodiment of the invention, the calculated transmission power Pifor a mesh Mi, (i=1 to n) is weighted by an attenuation parameter depending on the topography of said mesh Mi.

Said attenuation parameter is estimated when designing the CPC cell deployment and is stored in a look-up table.

With the method according to the invention, the probability of CPC detection is the same in all the meshes.

The invention is implemented by means of a base station comprising means for broadcasting a Cognitive Pilot Channel to a plurality of meshes Mi(i=1 to n) with a total transmission power P, n being the number of meshes in a geographical area, said Cognitive Pilot Channel transporting lists of information to said meshes to allow a User Equipment (UE) located in a given mesh Mi(i=1 to n) to select an operator and/or a Radio Access Technology and/or a communication frequency available in said given mesh Mi, said base station further comprises:means for determining for each mesh Mithe distance dito said base station,means for calculating for each mesh Mi(i=1 to n) a transmission power Pias a function of said distance diand of said total transmission power P,means for broadcasting to each mesh Mi(i=1 to n) said Cognitive Pilot Channel with the power Pi.

The base station according to the invention further comprises means for weighting the calculated transmission power Pifor a mesh Mi(i=1 to n) by an attenuation parameter depending on the topography of said mesh Mi.

The forgoing summary, as well as the following detailed description, will be better understood when read in conjunction with the appended figures illustrating an exemplary embodiment of the invention as follows.

DESCRIPTION OF EMBODIMENTS

The invention will be described when implemented in a geographical area2covered by at least one wireless telecommunication network and in which a Cognitive Pilot Channel is used for broadcasting information on the available Radio Access technologies (RATs) and frequencies to allow cognitive receiver such as mobile phones, PDA, or laptops to choose the most convenient RAT and frequency for communicating in the network. Said geographical area is divided into a number n of contiguous elementary meshes3.

As illustrated byFIG. 1, the geographical area2is divided into n=36 (thirty six) contiguous elementary meshes covered by a base station4that broadcasts the Cognitive Pilot Channel (CPC) carrying lists of information on operators, Radio Access Technologies and radio frequencies available for each mesh Mi(i=1 to 36).

The base station4comprises a processing module for estimating the path loss between the base station4and each mesh Mi(i=1 to 36).

Said path loss is defined at the definition phase of cells and the cellular network deployment as a function of the distance between each mesh Mi(i=1 to 36) and the base station4and as a function of the propagation environment.

The path loss calculated for each mesh Mi(i=1 to 36) is stored with the corresponding mesh Mi(i=1 to 36) in a look-up table10located in a storage module of the base station4.

FIG. 2is a flow chart illustrating the steps of the method according to the invention.

At step20, for each mesh Mi(i=1 to 36) the processing module determine the list of information to broadcast in said mesh Mi.

At step22, the processing module reads path loss for the mesh Mi(i=1 to 36) from the look-up table10.

At step24, the processing module reads the total available power P and transmits, at step26, the CPC message with a power given by the formula: Pi-P*Path loss/n, where n is the number of meshes (n=36 in the example ofFIG. 1).

The processing module increments i at step28and re-runs the method from step20until all the meshes Mi(i=1 to n) receive the appropriate information with the appropriate power Pi.