Patent ID: 6307851
Filing Date: 2001-10-23
Classification: H04B,H04L

Abstract:
A system for transmitting digital signals by radio between a plurality of subscriber stations and a base station using the so-called MC-CDMA (Multicarrier--Code Division Multiple Access) method in which a plurality of useful links are processed simultaneously in a common RF frequency band, comprising:data blocks of finite length, which can be represented by data vectorsd.sup.(k) =(d.sub.1.sup.(k),d.sub.2.sup.(k) . . . d.sub.N.sup.(k)).sup.T, d.sub.n.sup.(k).epsilon.C, k=1 . . . K, n=1 . . . N, K,N .epsilon. IN,each of the data vectors being composed of N complex data symbols d.sub.n.sup.(k) to the base m with a data symbol period length T.sub.s ; K subscriber stations for transmitting the data blocks with application of a spread code, assigned to a respective subscriber station k, k=1 . . . K, with Q subcarriers distributed uniformly within an RF radio frequency band;a reception site using said spread code and a CDMA detector device for decoding the data blocks;a number of data symbols d.sub.n.sup.(k) transmitted simultaneously by a specific subscriber station k being one and all the data symbols d.sub.n.sup.(k) of a subscriber station being transmitted successively; said transmission using the Q subcarriers of bandwidth B.sub.s =B.sub.U /Q=1/T.sub.s, the subcarriers numbered with g=1 . . . Q each having a single center of frequency f.sub.q, q=1 . . . Q, in accordance with ##EQU39##each data symbol d.sub.n.sup.(k) of a subscriber station being spread over all the Q subcarriers of the bandwidth B.sub.s by a subscriber-specific signature code sequencec.sup.(k) =(c.sub.1.sup.(k), c.sub.2.sup.(k) . . . c.sub.Q.sup.(k)).sup.T, c.sub.q.sup.(k).epsilon.C, k=1 . . . K, q=1 . . . Q, K, Q.epsilon.INcomposed of chips c.sub.q.sup.(k), each chip being assigned to a particular subcarrier; a linearly modulated signal, which is transmitted by a subscriber station, k, k=1 . . . K which is given in the equivalent low-pass filter region by ##EQU40##linear MC-CDMA spread modulation being formed by samplings of a c.sup.(k) (t;c.sup.(k)) made at a rate 1/T.sub.c, the sampled values .zeta..sub.q.sup.(k), q=1 . . . Q, K produced by these samplings giving rise to vectors.zeta..sup.(k) =(.zeta..sub.1.sup.(k), .zeta..sub.2.sup.(k) . . . .zeta..sub.Q.sup.(k)).sup.T, .zeta..sub.q.sup.(k).epsilon.C, k=1 . . . K, q=1 . . . Q, K, Q.epsilon.IN;a relation between the vectors .zeta..sup.(k) and the spread code vectors c.sup.(k) being given the equation .zeta..sup.(k) =Dc.sup.(k) with a matrix ##EQU41##of an inverse discrete Fourier transformation (IDFT), a vector matrix .zeta..sup.(k) containing Q column vectors ##EQU42##.alpha.=1 . . . Q, so that D=(.delta..sup.(1), .delta..sup.(2) . . . .delta..sup.(Q))and thus.zeta..sup.(k) =(c.sub.1.sup.(k).delta..sup.(1) +c.sub.2.sup.(k).delta..sup.(2) + . . . +c.sub.Q.sup.(k).delta..sup.(Q))is obtained;since each chip c.sub.q.sup.(k) is assigned to a particular subcarrier q, the equation .zeta..sup.(k) =Dc.sup.(k) is interpreted such that columns .delta..sup.(q), q=1 . . . Q of the matrix D represent the Q subcarriers and rows of the matrix D represent Q time moments within the data symbol period length T.sub.s during which sampled values are taken; anda result of the equation .zeta..sup.(k) =Dc.sup.(k) being a vector .zeta..sup.(k) with elements .zeta..sub.g.sup.(k) which result from a linear combination of the chips c.sub.q.sup.(k).