A method of producing a chip block for wireless transmission in a Direct Sequence Code Division Multiple Access, DS-CDMA, communication system, the method comprising: producing, by a processor (3, 8) associated with a transmitter (2, 10), the chip block by: spreading a symbol over at least one chip block; segmenting the chip block to form a first sub-block (a 0;a 15) of the chip block, said first sub-block (a 0;a 15) being arranged for containing a first number of chips; segmenting the chip block to form a second sub-block (a 0;a 15) of the chip block, said second sub-block (a 0;a 15) being separate from said first sub-block (a 0;a 15) and being arranged for containing a second number of chips; and arranging a first sub-sequence (18;19) of chips furthest to a first end of the chip block in the first sub-block (a 0;a 15), which first sub-sequence is identical to a second sub-sequence (18; 19) furthest to a second end of the chip block in the second sub-block (a 0;a 15), whereby the sub sequences (18;19) form a cyclic prefix of the chip block; characterized in that, the method further comprises: modifying at least one chip contained in the first sub-block (a 0;a 15) and not being part of the first sub-sequence (18; 19), the modifying being dependent on said first sub-sequence (18;19) such that the symbol can be at least partially despread from the chip block; and transmitting, by the transmitter (2, 10), the produced chip block over a radio interface of the communication system. producing, by a processor (3, 8) associated with a transmitter (2, 10), the chip block by: spreading a symbol over at least one chip block; segmenting the chip block to form a first sub-block (a 0;a 15) of the chip block, said first sub-block (a 0;a 15) being arranged for containing a first number of chips; segmenting the chip block to form a second sub-block (a 0;a 15) of the chip block, said second sub-block (a 0;a 15) being separate from said first sub-block (a 0;a 15) and being arranged for containing a second number of chips; and arranging a first sub-sequence (18;19) of chips furthest to a first end of the chip block in the first sub-block (a 0;a 15), which first sub-sequence is identical to a second sub-sequence (18; 19) furthest to a second end of the chip block in the second sub-block (a 0;a 15), whereby the sub sequences (18;19) form a cyclic prefix of the chip block; spreading a symbol over at least one chip block; segmenting the chip block to form a first sub-block (a 0;a 15) of the chip block, said first sub-block (a 0;a 15) being arranged for containing a first number of chips; segmenting the chip block to form a second sub-block (a 0;a 15) of the chip block, said second sub-block (a 0;a 15) being separate from said first sub-block (a 0;a 15) and being arranged for containing a second number of chips; and arranging a first sub-sequence (18;19) of chips furthest to a first end of the chip block in the first sub-block (a 0;a 15), which first sub-sequence is identical to a second sub-sequence (18; 19) furthest to a second end of the chip block in the second sub-block (a 0;a 15), whereby the sub sequences (18;19) form a cyclic prefix of the chip block; characterized in that, the method further comprises: modifying at least one chip contained in the first sub-block (a 0;a 15) and not being part of the first sub-sequence (18; 19), the modifying being dependent on said first sub-sequence (18;19) such that the symbol can be at least partially despread from the chip block; and transmitting, by the transmitter (2, 10), the produced chip block over a radio interface of the communication system. modifying at least one chip contained in the first sub-block (a 0;a 15) and not being part of the first sub-sequence (18; 19), the modifying being dependent on said first sub-sequence (18;19) such that the symbol can be at least partially despread from the chip block; and transmitting, by the transmitter (2, 10), the produced chip block over a radio interface of the communication system.