Biphase Code Detection for Differential Manchester Encoded Signals in Digital Communications

S. Vasana (USA)


Manchester Code, Diphase Code, Demodulation and Detection, Wireless Communication


The differential Manchester code (also called Diphase code) is specified in the IEEE802.5 standard for token ring LANs, and is used for many other applications, including magnetic and optical storage. The Manchester code has been specified for the IEEE 802.3 standard for baseband coaxial cable and twisted-pair Carrier Sense Multiple Access/Collision Detection (CSMA/CD) bus LANs. Both kinds of Manchester coded signals are widely used in computer digital communications and wireless communications, e.g. EtherNet. However, the system using Manchester code or differential Manchester code modulated signals loses 3 dB in sensitivity if using the same usual detection method as it is to original signal without using the codes. This paper proposes a special demodulation/detection method to detect the Manchester or Diphase code modulated signal, which is called delta detection and is recently patented [1]. The system can gain back up to 3dB sensitivity when the delta detection is used. This delta detector utilizes the incoming signal energy more efficiently, resulting in a lower required transmission power and/or higher detection sensitivity. The simulation of demodulation/detection system for Manchester code modulated signal presented in the paper realized this method and confirmed the expected results.

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