Error rate performance of NEC receivers of Duoquaternary FSK

Abstract

Wireless communications have become indispensable and spectrum resources have already reached their limits. Specialcare needs to be taken for constant envelope modulations that can achieve higher bandwidth efficiency while keepingcircuitry at simple levels. Partial response signalling and correlative encoding are techniques that maintain im~munityto non1inearities due to constant envelope property as well as high bandwidth efficiency. Duoquaternary frequencyshift keying (FSK) makes use of correlative encoding and premodulation filtering to increase spectrum efficiency inaddition to having better power efficiency than MSK. Therefore, it should be considered for applications in mobile,portable and/or fixed digital data transmission systen1s. This type of signaling, apart from reducing the out-of-bandpower levels, helps increase the symbol error rate. Nonredundant error correction (NBC) is utilised to improve thesystem perfonnance under white gaussian noise conditions. The receiver consists of a band of differential detectors. Itutilises their outputs to correct data patterns containing random errors in accordance with the concept of a convolutionalerror-correcting code without sacrificing any more bandwidth or power.In this paper, a single- and a double-error-correcting receiver of duoquatemary FSK are proposed. For the firsttime correlative multilevel modulations of higher efficiency are theoretically evaluated with NEC in additive whitegaussian noise environments. Computer-simulated results of SER performance are also given, indicating significantperformance improvements over conventional differential detection.