Global Navigation Satellite System (GNSS) refers to multi-constellation satellite basednavigation systems including GPS, GLONASS, BeiDou, Galileo, NavIC and QZSS as well assatellite-based augmentation systems. The developments in GNSS chip onto smart devices hashelped GNSS reach millions of users worldwide. While positioning accuracy at the meter ortens of meter level, referred to asstandard positioning, is adequate for vehicle navigation basedapplication like fleet management and emergency services like E-911, sub-meter-level accuracy,referred to asprecise positioning, is desirable for applications like precision farming, self-drivingvehicle and machine control. The thesis work explores the possibility of exploiting existing GNSScivil signal observables like pseudorange, Doppler and carrier-phase to derive computationallyefficient precise positioning solutions for the real-time applications.In this work a novel pseudorange computation algorithm based on fine code-phasemeasurement using carrier-phase observable is proposed. The proposed algorithm achievesa sub-meter-level accuracy with a convergence time of the fraction of a second. This precisepositioning algorithm will be useful for applications having stringent latency requirements. Asof today best known precise positioning solutions provide sub-centimeter level accuracy but withaconvergencetimeofseveralminutes, renderingthemunsuitableforlowlatencyapplications. Theproposed solution does not require any hardware modifications for the GNSS receiver chip. SinceGNSS measurements from smart-phones and tablets running the Android N are now availableto the users, the proposed solution can be integrated in a smart device through software to getsub-meter-level accuracy for positioning solutions.