# Patent

## Title
Method for controlling the power for broadcasting a Cognitive Pilot Channel

## Abstract

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.

## Background
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 Mi with 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 Mi with 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 di to said base station,
        calculating for each mesh Mi (i=1 to n) a transmission power Pi as a function of said distance di and 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 Pi is inversely proportional to said distance di.
According to a preferred embodiment of the invention, the calculated transmission power Pi for 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 Mi the distance di to said base station,
        means for calculating for each mesh Mi (i=1 to n) a transmission power Pi as a function of said distance di and 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 Pi for 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.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 schematically represents a geographical area comprising meshes in which the method according to the invention is implemented;
FIG. 2 is flow chart illustrating the steps of the method according to the invention.



DESCRIPTION OF EMBODIMENTS
The invention will be described when implemented in a geographical area 2 covered 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 meshes 3.
As illustrated by FIG. 1, the geographical area 2 is divided into n=36 (thirty six) contiguous elementary meshes covered by a base station 4 that 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 station 4 comprises a processing module for estimating the path loss between the base station 4 and 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 station 4 and 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 table 10 located in a storage module of the base station 4.
FIG. 2 is a flow chart illustrating the steps of the method according to the invention.
At step 20, for each mesh Mi (i=1 to 36) the processing module determine the list of information to broadcast in said mesh Mi.
At step 22, the processing module reads path loss for the mesh Mi (i=1 to 36) from the look-up table 10.
At step 24, the processing module reads the total available power P and transmits, at step 26, 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 of FIG. 1).
The processing module increments i at step 28 and re-runs the method from step 20 until all the meshes Mi (i=1 to n) receive the appropriate information with the appropriate power Pi.

## Claims

1. A method for controlling the power for broadcasting a Cognitive Pilot Channel transporting 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 (2) including at least one base station broadcasting the Cognitive Pilot Channel to the meshes Mi (i=1 to n), performed in the base station the method comprising:
calculating for each mesh Mi (i=1 to n) a transmission power Pi; and
broadcasting to each mesh Mi (i=1 to n) the Cognitive Pilot Channel with the power Pi from the base station,
wherein each of powers Pi (i=1 to n) is calculate as a function of a path loss between each mesh and the base station, and
wherein the path loss is calculated as a function of distance di between each mesh and the base station.

2. The method according to claim 1 wherein the power Pi is inversely proportional to the distance di.

3. The method according to claim 2 wherein the power Pi is calculated as a function of a total transmission power P.

4. The method according to claim 3 wherein the power Pi is calculated by the following formula:


Pi=P*Path loss/n where n is the number of meshes.

5. The method according to claim 1 wherein the calculated transmission power Pi for a mesh Mi (i=1 to n) is weighted by an attenuation parameter depending on the topography of the mesh Mi (i=1 to n).

6. The method according to claim 5 wherein attenuation parameter is estimated when designing the CPC cell deployment and stored in a look-up table.

7. A base station comprising means for broadcasting a Cognitive Pilot Channel transporting 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 (2) including at least one base station broadcasting the Cognitive Pilot Channel to the meshes Mi (i=1 to n), the base station further comprising:
calculation means for calculating for each mesh Mi (i=1 to n) a transmission power Pi; and
means for broadcasting to each mesh Mi (i=1 to n) the Cognitive Pilot Channel with the power Pi,
wherein the calculation means calculates each of powers Pi (i=1 to n) as a function of a path loss between each mesh and the base station, and
wherein the base station further comprises means for calculating the path loss as a function of distance di between each mesh and the base station.

8. The base station according to claim 7 further comprising means for weighting the calculated transmission power Pi for a mesh Mi (i=1 to n) by an attenuation parameter depending on the topography of the mesh Mi.