Method for the transmission of reference signals in an OFDM system

Method for digital signal transmission in frames having a multiplicity of modulated carriers, a zero symbol and a time frequency phase reference symbol, comprising the steps of:

• modulating the signal using CAZAC sequences, wherein the time frequency phase reference symbol is also modulated by at least one pseudorandom sequence having a greater length than the CAZAC sequences;
• arranging the sequences having a greater length being arranged in the outer carriers at the lowest and at the highest carrier frequencies;
• performing rough synchronization by means of the zero symbol, and
• performing synchronization by evaluation of the time frequency phase reference symbol.

Device for decoding a digital signal which is transmitted in frames using a multiplicity of modulated carriers, a zero symbol and a time frequency phase reference signal which is modulated by CAZAC sequences, the device comprising:

• demodulation means for demodulating a received signal;
• a zero signal component detector means coupled to said demodulation means for detecting the zero symbol;
• an OFDM decoder means coupled to said demodulation means for decoding a carrier demodulated received signal;
• a digital synchronization evaluation means coupled to said demodulation means for evaluating an initially demodulated received signal, which are controlled by an output signal of the zero signal component detector means and which control the OFDM decoder means and which additionally evaluate either a further reference symbol which is modulated by at least one pseudorandom sequence having a greater length than any of the CAZAC sequences, or said time frequency phase reference signal, which is also modulated by at least one pseudorandom sequence having a greater length than any of the CAZAC sequences, these sequences having a greater length being arranged essentially in the outer carriers at a lowest and at a highest carrier frequencies.

Method for digital signal transmission in frames having a multiplicity of modulated carriers and having a synchronization symbol which is spread over the bandwidth of the signal, the power of the signal being zero or virtually zero for a zero part of the duration of the synchronization symbol, comprising the steps of:

• using during a further time segment of a frame a modulation which differs from the modulation of the remaining signal part of that frame, for every other carrier, with half the effective symbol length;
• transmitting in the signal part of the synchronization symbol at least one bit sequence having optimum autocorrelation properties, the information sequence of the bit sequence being assigned to the carriers in order from the lowest to the highest frequency or vice versa;
• performing a rough synchronization that can take place in a receiver on the basis of the part-symbol with zero power, and
• performing after the valuation of the received signal component of the synchronization symbol on the basis of the rough synchronization, a more precise determination of the time period of the symbol or several of such symbols.

Device for decoding a digital signal which is transmitted in frames having a multiplicity of modulated carriers and having a synchronization symbol component which is spread over the bandwidth of the signal, the power of the signal being zero or virtually zero before a zero part of the duration of the synchronization symbol, the device comprising:

• demodulation means for demodulating a received signal;
• a zero signal component detector means for detecting the zero part;
• an OFDM decoder means coupled to said demodulation means for OFDM decoding a carrier demodulated received signal;
• digital synchronization evaluation means coupled to said demodulation means for synchronizing an initially demodulated received signal, which are controlled by an output signal of the zero signal component detector means and which control the OFDM decoder means;
• and
• said synchronization symbol signal component being converted into frequency domain form in an FFT circuit in said digital synchronization evaluation means, then being complex-conjugate multiplied in a further stage of a desired sequence stored in the device and being transformed back into time domain form in an FFT−1 stage, to thereby produce a resulting channel impulse providing a precise determination of a time period of said synchronization symbol component.