A METHOD, BASE STATION AND USER EQUIPMENT FOR REDUCING A COGNITIVE PILOT CHANNEL BANDWIDTH DESCRIPTION

Background of the invention Field of the invention

The invention pertains to telecommunication field and concerns a method for reducing a Cognitive Pilot Channel (CPC) bandwidth used for transmitting lists of information to a plurality of meshes of a geographical area comprising at least one base station covering said plurality of meshes to allow a User Equipment camping on a given mesh among said plurality of meshes to select an operator and/or an access technology and/or a communication frequency available in said given mesh.

The invention also concerns a base station covering a geographical area comprising a plurality of meshes receiving a Cognitive Pilot Channel (CPC) carrying lists of information on operators, access technology and radio frequencies available in each mesh.

The invention further concerns User Equipment (UE) camping on a mesh of a geographical area comprising a plurality of meshes receiving a Cognitive Pilot Channel (CPC) carrying lists of information on operators, access technology and radio frequencies available in each mesh.

Description of the related 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.

- Mesh based concept in which a cell in the geographical area is divided into a plurality of meshes and information is provided about operators, RAT and Frequencies available in each mesh.

- Optimised broadcast concept in which information about all the RATs and frequencies available in the cells is transmitted.

Although Mesh based concept is more precise than Optimised broadcast concept, it presents a drawback resulting from the fact that the transmission of information to the meshes requires a larger frequency band to be allocated to CPC.

One of the proposed methods to reduce the CPC data rate is to transmit the same CPC for the whole cell, not to meshes of said cell, and transmit the coverage area for each technology and frequency. The problem with this kind of approach is that coverage areas are not easily characterized and transmitting a detailed coverage area may result in a large data-rate as well.

The present invention aims at reducing the CPC data rate.

Another object of the invention is to reduce the CPC message length to enable a shorter period between mesh information occurrences for the same bit rate.

The invention also aims at reducing the required bandwidth for the CPC use while increasing CPC message robustness.

Summary of the invention

The invention is based on the fact that close meshes usually differ by only few frequencies. Thus instead of transmitting the whole information each time, in the method according to the invention, all the information is first transmitted to a reference mesh, and only information about the difference between each mesh is subsequently transmitted to a given mesh.

This object is achieved by means of a method for reducing a Cognitive Pilot Channel (CPC) bandwidth used for transmitting lists of information to a plurality of meshes of a geographical area comprising at least one base station covering said plurality of meshes to allow a User Equipment camping on a given mesh among said plurality of meshes to select an operator and/or an access technology and/or a communication frequency available in said given mesh.

The method according to the invention comprises the following steps:

- providing the base station with said lists of information,

- defining a reference list of information associated to a reference mesh,

- associating an identifier to said reference mesh,

- transmitting the reference list of information to the reference mesh, and for each subsequent transmission of information to a given mesh,

- comparing the list of information intended for said given mesh to the list of information comprised in the reference list,

- determining from said comparison a difference between the list of information intended for said given mesh and the list of information comprised in the reference list,

- transmitting to said given mesh the identifier of the reference mesh along with the determined difference, and,

- upon reception of said identifier and said difference, the User Equipment automatically infers a complete list of operators, technologies and frequencies available in said given mesh from the difference between the list of information intended for said given mesh and the reference list.

According to a first variant of the invention,

- For i=2 to n, n being the number of meshes in the geographical area, the base station receives information about the operators, the technologies and the frequencies present in each mesh and selects mesh #1 as a reference mesh,

- the base station transmits the complete list of information concerning operators, Radio Access technologies (RAT) and frequencies present in the reference mesh #1,

- For i=2 to n, n being the number of meshes in geographical area, the base station compares information intended respectively for the mesh #i and mesh #i-l and derives the differences between the list of information of each mesh and the following mesh,

- the base station transmits said difference to the mesh #i,

- upon reception of said difference, the User Equipment analyses the information intended for the reference mesh, and,

- For i=2 to m, where m is the rank of the mesh in which the UE is located, the UE determines the list of operators, RATs and frequencies present in mesh #m by including all the differences between consecutive meshes.

According to a second variant of the invention,

- the base station receives information about the operators, the technologies and the frequencies present in each mesh.

- For i=l to n, n being the number of meshes in the geographical area, the base station compares the list of information intended for a given mesh #m (l