Soft decision differential demodulator for radios in wireless networks supporting train control
OwnerVafa Ghazi-Moghadaminventor
Life of this patent
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Abstract
Improvements to demodulators in receivers of radios used for train communications t to receive a radio frequency (RF) signal transmitting a packet of data. A demodulator is configured to generate a soft decision for a decoder, the soft decision including reliability information determined by calculating for the bit position a logarithmic likelihood ratio (LLR). The demodulator is configured to correct a bias in the LLR calculation for any one of the bit positions resulting from a difference in the number symbols in the set of all possible symbols that could have a 0 value in the bit position and the set of all possible symbols that could have a 1 in the bit position.
Claims8
A radio for communicating over a wireless network supporting train control, the radio comprising a receiver configured to receive a radio frequency (RF) signal transmitting a packet of data comprising a sequence of bits using a modulation scheme providing for at least 16 possible discrete symbols, each symbol comprising a group of at least 4 bits, each of the at least 4 bits occupying a predefined bit position in the symbol;
- the receiver comprising:
- a demodulator configured to demodulate the RF signal according to the modulation scheme and generate for each received symbol a soft decision of which of the at least 16 possible discrete symbols was received;
- and
- a decoder configured to decode the soft decisions to recover the data in the packet;
- wherein the demodulator is configured to generate a soft decision by generating for received symbol a bit value and reliability information reflecting a probability of the bit value being correct, the reliability information determined by calculating for the bit position a logarithmic likelihood ratio (LLR) of the probability of the bit value being 0 given the received symbol to the probability of the bit value being a 1 given the received symbol, the LLR being calculated on a basis of all possible symbols that could have a 0 value in the bit position and all possible symbols that could have a 1 value in the bit position;
- and
- wherein the demodulator is further configured to correct a bias in the LLR calculation for any one of the bit positions resulting from a difference in the number symbols in a first set of all possible symbols that could have a value of 0 in the bit position and a second set of all possible symbols that could have a value of 1 in the bit position.
A method for communicating over a wireless network supporting train control, the method comprising:
- receiving a radio frequency (RF) signal transmitting a packet of data comprising a sequence of bits using a modulation scheme that provides for at least 16 possible discrete symbols, each symbol comprising a group of at least 4 bits, each of the at least 4 bits occupying a predefined bit position in the symbol;
- demodulating the RF signal according to the modulation scheme and generating for each received symbol a soft decision of which of the at least 16 possible discrete symbols was received;
- and
- decoding the soft decisions to recover the data in the packet;
- wherein demodulating comprises,
- generating for received symbol a bit value and reliability information reflecting a probability of the bit value being correct, the reliability information determined by calculating for the bit position a logarithmic likelihood ratio (LLR) of the probability of the bit value being 0 given the received symbol to the probability of the bit value being a 1 value given the received symbol, the LLR being calculated on a basis of all possible symbols that could have a 0 value in the bit position and all possible symbols that could have a 1 in the bit position;
- and
- correcting a bias in the LLR calculation for any one of the bit positions resulting from a difference in the number symbols in a first set of all possible symbols that could have a value of 0 in the bit position and a second set of all possible symbols that could have a value of 1 in the bit position.
Dependencies are inferred from the claim text.