Third-generation TDRSS-compatible direct-sequence spread-spectrum digital receiver

A digital communication receiver, called a third-generation receiver, has been developed. This receiver takes samples of the direct-sequence spread signal at a nonzero intermediate frequency (IF) instead of the zero IF (baseband), and quantizes the samples by employing a 1-b analog-to-digital (A/D) converter at the receiver front end. These 1-b samples are digitally processed for pseudonoise (PN) code, carrier, bit synchronization, and bit decision with the use of an application-specific integrated circuit. The effects of the IF sampling and 1-b A/D conversion on PN code synchronization are analyzed for a PN spread-spectrum communication system with oversampling rate, e.g., 12 samples per chip. In addition, the bit-error rate (BER) degradation due to the 1-b A/D conversion is studied by assuming perfect PN code, carrier, and bit synchronization. It is observed that the BER degradation due to the 1-b A/D is significant, e.g., 2.4 dB, when decimation is made after IF sampling such that only one sample per chip is used for bit decision. These analyzed BER results agree well with the simulated results. However, if no decimation is made and oversampling is used for bit decision, BER degradation due to 2-b A/D conversion is insignificant, e.g., 0.6 dB.