Cell search method for a downlink channel of an OFDMA transmission system
A cell search method in a multiple carrier wireless network includes a step of trying to select, among a list of candidate couples [carrier frequency; bandwidth], at least one candidate associated with at least one cell of the multiple carrier wireless network. The cell search method includes: a step of obtaining and ordering an initial list of possible candidate couples [carrier frequency; bandwidth] according to the multiple carrier wireless network; a step of reducing the initial list, delivering a reduced list, the reduced list including only candidates compatible with a predetermined communication mode of the multiple carrier wireless network, through a differential cross correlation of the candidate couples [carrier frequency; bandwidth] of the initial list; a cell search step in which a cross-correlation is performed by testing all time/frequency hypothesis for at least one candidate of the reduced list of candidates, delivering synchronisation information.
1. A cell search method in a multiple carrier wireless network, said method comprising:
a step of obtaining and/or ordering an initial list of possible candidate couples, [carrier frequency; bandwidth], by an apparatus according to said multiple carrier wireless network;
a step of reducing said initial list by the apparatus, delivering a reduced list of candidate couples, said reduced list comprising only the candidate couples of the initial list that are compatible with a predetermined communication mode of said multiple carrier wireless network, wherein said step of reducing said initial list comprises for at least some candidate couples of said initial list, an OFDMA processing step, in which a preamble is searched in view of a given number of symbols applied to a received signal at values of a current candidate couple, said search being made by calculating a differential cross correlation C, between a differential received vector, calculated from said received signal, and a differential preamble vector; and
a step of searching, among the reduced list of candidate couples [carrier frequency; bandwidth], for at least one candidate couple associated with at least one cell of said multiple carrier wireless network and, if identified, selecting the at least one candidate couple associated with the at least one cell of said multiple carrier wireless network.
2. The cell search method according to claim 1 , wherein each element of said reduced list comprises, in addition to carrier frequency and bandwidth, a base station identifier and/or a frame preamble number.
3. The cell search method according to claim 1 , wherein said step of reducing said initial list comprises, for a current candidate couple of said initial list:
an RF settings step of adjusting reception parameters of the received signal;
at least one step of detecting, for said current candidate couple, a presence of a preamble, representative of said communication mode, among a plurality of assumed symbol extracted from a received signal; and
a decision step wherein said current candidate couple is inserted in said reduced list when at least one presence of one preamble has been detected.
4. The cell search method according to claim 3 , wherein said step of detecting a presence of a preamble comprise a step of calculating one differential cross correlation C per symbol k of said plurality of assumed symbol, said differential cross correlation C, being a correlation between a differential received vector and a differential preamble vector, and wherein said current candidate couple is inserted in said reduced list when at least one of said cross correlations C exceeds a predetermined threshold Th.
5. The cell search method according to claim 1 , wherein said step of obtaining and/or ordering said initial list of possible candidate couples [carrier frequency; bandwidth] comprises a step of ordering said initial list according to a communication standard.
6. The cell search method according to claim 1 , wherein said step of obtaining and/or ordering said initial list of possible candidate couples [carrier frequency; bandwidth] comprises an initial scan step in which said candidate couples are detected and ordered by means of power detection.
7. An apparatus for searching cell in a multiple carrier wireless network, said apparatus comprising:
means for obtaining and/or ordering an initial list of possible candidate couples [carrier frequency; bandwidth] according to said multiple carrier wireless network;
means for reducing said initial list, delivering a reduced list of candidate couples, said reduced list comprising only candidate couples of the initial list that are compatible with a predetermined communication mode of said multiple carrier wireless network, wherein reducing said initial list comprises for at least some candidate couples of said initial list, an OFDMA processing step, in which a preamble is searched in view of a given number of symbols applied to a received signal at the values of a current candidate couple, said search being made by calculating a differential cross correlation C, between a differential received vector, calculated from said received signal, and a differential preamble vector; and
means for searching, among the reduced list of candidate couples [carrier frequency; bandwidth], for at least one candidate couple associated with at least one cell of said multiple carrier wireless network and, if identified, selecting the at least one candidate couple associated with the at least one cell of said multiple carrier wireless network.
8. A mobile station comprising the cell search apparatus according to claim 7 .
9. A non-transitory computer-readable support comprising a computer program product stored thereon, said computer program product comprising program code instructions for performing a cell search method in a multiple wireless network, when executed by a processor, wherein the method comprises:
a step of obtaining and/or ordering an initial list of possible candidate couples [carrier frequency; bandwidth] by the processor according to said multiple carrier wireless network, said initial list comprising candidate couples;
a step of reducing said initial list by the processor, delivering a reduced list of candidate couples, said reduced list comprising only the candidate couples of the initial list that are compatible with a predetermined communication mode of said multiple carrier wireless network, wherein said step of reducing said initial list comprises for at least some candidate couples of said initial list, an OFDMA processing step, in which a preamble is searched in view of a given number of symbols applied to a received signal at the values of a current candidate couple, said search being made by calculating a differential cross correlation C, between a differential received vector, calculated from said received signal, and a differential preamble vector; and
a step of searching, among the reduced list of candidate couples [carrier frequency; bandwidth], for at least one candidate couple associated with at least one cell of said multiple carrier wireless network and, if identified, selecting the at least one candidate couple associated with the at least one cell of said multiple carrier wireless network.