Synchronization method and apparatus for modems based on jointly iterative turbo demodulation and decoding

A modem using iterative turbo coding, a carrier and time tracking algorithm, and continuous phase modulation, said modem comprising:

• a multiplier for multiplying an input signal having coded information bits and a carrier by a phase signal;
• a demodulator branch metric computer connected the multiplier for demodulating the multiplied input signal;
• a correlator bank connected to the multiplexer for providing correlator phase estimates;
• an inner code a posterior probability (APP) decoder connected to the demodulator branch metrics computer for delivering alpha values representative of data symbols hard decision phase start information, and a decoder metrics output at a high error rate and low latency wherein the alpha values select a correlator phase estimate from the correlator bank;
• a symbol phase error estimator for producing a symbol phase error estimate from the correlator phase estimate and the hard decision phase information;
• a carrier tracking loop filter for receiving the symbol phase error estimate and providing an output frequency;
• and
• a numerically controlled oscillator for receiving the output frequency from the carrier tracking loop filter and providing the phase signal to the multiplier to multiply the input signal to track the input carrier.

A bandwidth efficient advanced modulation waveform modem using iterative turbo coding and continuous phase modulation said modem having a demodulator comprising a turbo decoder and a decision feedback carrier and time tracking algorithm, said modem comprising:

• an a posteriori probability (APP) decoder utilized as a decision device for providing symbol decisions at a high error rate and low latency for a coded input data stream having a carrier, said APP decoder providing a decoder metrics output confidence level and operating with a reduced traceback depth to reduce latency;
• a symbol phase estimator for producing a symbol phase error estimate from the symbol decisions;
• an erasure decision function for deciding which symbol decisions are correct and which symbol decisions are erasures, said erasure decision function comparing the decoder metrics output confidence level from the APP decoder to a confidence threshold and the phase error estimate from the symbol phase error estimator with a phase threshold;
• an erasure logic function that maintains knowledge of a last phase error and generates a next symbol phase error estimate;
• a multiplexer connected to the erasure decision function and erasure logic function that passes the symbol phase error estimate when the thresholds are met and the symbol decision is accented as correct, passes the symbol phase error estimate when the thresholds are not met but symbol decision is accepted as correct, and inhibits the symbol phase error estimate when the threshold is not exceeded and an erasure is declared;
• and
• a carrier tracking function for receiving the symbol phase error estimates when the symbol decisions are correct and receiving an erasure input when the symbol decisions are erasures to maintain carrier tracking.

A bandwidth efficient advanced modulation waveform modem using iterative turbo coding and continuous phase modulation said modem having a demodulator comprising a turbo decoder and a carrier and time tracking algorithm said carrier and time tracking algorithm performing the steps comprising:

• multiplying an input signal having coded information bits and a carrier in a multiplier;
• demodulating the multiplied input signal in a branch metric computer connected to the multiplier;
• providing correlator phase estimates from a correlator bank connected to the multiplier;
• delivering alpha values representative of date symbols, hard decision phase information, and a decoder metrics output confidence levels at a high error rate and low latency from an inner code a posteriori probability (APP) decoder connected to the branch metric computer;
• selecting correlator phase estimates from the correlator bank in a multiplexer with the alpha values from the inner code APP decoder;
• producing a symbol phase error estimate from the correlator phase estimate and the hard decision phase information in a symbol phase estimator;
• providing an output frequency proportional to the symbol phase error estimate from a carrier tracking loop filter;
• and
• providing a phase signal from a numerically controlled oscillator to the multiplier to multiply the input signal to track the input carrier.