A spread spectrum communications system, comprising; a plurality of user equipments; and a base station to transmit data symbols to each user equipment in parallel on a plurality of sub-carrier frequencies and at regular temporal positions during a transmission of a data chunk; wherein the data symbols comprise first pilot symbols adaptive to said each user equipment, wherein the first pilot symbols selectively replace part of the data symbols according to the speed of said each user equipment and second pilot symbols fixed to the plurality of user equipments, wherein the second pilot symbols are allocated at the beginning of the data chunk and arranged in a fixed structure spread over all sub-carrier frequencies; wherein the base station transmits to said each user equipment pilot symbol information identifying a location of the first pilot symbols in the data chunk, and wherein said each user equipment utilizes the first pilot symbols for channel estimation; and wherein the first pilot symbols are inserted, at a central sub-carrier frequency of the data chunk, along the time domain separated by a temporal distance 2 x N T where: N T = ⌊ 1 2. f D. T sym ⌋ where └ ┘ is a round down to the nearest integer where f D is the Doppler frequency measured at the user equipment in Hz; and where T sym is the data symbol duration in seconds; and wherein the first pilot symbols selectively replace part of the data symbols by a frequency spacing N F N F = ⌊ 1 2. ⁢ Δ f. τ max ⌋ where └ ┘ is a round down to the nearest integer where Δ f is the sub-carrier bandwidth in Hz, and where τ max is the maximum delay spread in seconds. a plurality of user equipments; and a base station to transmit data symbols to each user equipment in parallel on a plurality of sub-carrier frequencies and at regular temporal positions during a transmission of a data chunk; wherein the data symbols comprise first pilot symbols adaptive to said each user equipment, wherein the first pilot symbols selectively replace part of the data symbols according to the speed of said each user equipment and second pilot symbols fixed to the plurality of user equipments, wherein the second pilot symbols are allocated at the beginning of the data chunk and arranged in a fixed structure spread over all sub-carrier frequencies; wherein the base station transmits to said each user equipment pilot symbol information identifying a location of the first pilot symbols in the data chunk, and wherein said each user equipment utilizes the first pilot symbols for channel estimation; and wherein the first pilot symbols are inserted, at a central sub-carrier frequency of the data chunk, along the time domain separated by a temporal distance 2 x N T where: N T = ⌊ 1 2. f D. T sym ⌋ where └ ┘ is a round down to the nearest integer where f D is the Doppler frequency measured at the user equipment in Hz; and where T sym is the data symbol duration in seconds; and where └ ┘ is a round down to the nearest integer where f D is the Doppler frequency measured at the user equipment in Hz; and where T sym is the data symbol duration in seconds; and wherein the first pilot symbols selectively replace part of the data symbols by a frequency spacing N F N F = ⌊ 1 2. ⁢ Δ f. τ max ⌋ where └ ┘ is a round down to the nearest integer where Δ f is the sub-carrier bandwidth in Hz, and where τ max is the maximum delay spread in seconds. where └ ┘ is a round down to the nearest integer where Δ f is the sub-carrier bandwidth in Hz, and where τ max is the maximum delay spread in seconds.