Novel soft-bit demodulator with multidimensional projection for high-order modulation

The demand of higher data rates for wireless applications is unlimited. To provide spectral efficiency and flexible data rate services, the modulation alphabets and channel coding rates can be adapted by link quality control according to the evolutions of 3G standardizations including EDGE and WCDMA. A novel multidimensional projection-based soft-bit demodulator is proposed for high-order modulations. Multiple dimensions are set up based on the alphabet size of modulations, the hard-decision and its nearest constellation points in Euclidean distance. The hard decision at each corresponding constellation point is multiplied by the projection amplitude on each dimension as the reliability, linearly combined, and then fed to the soft-decision channel decoder. The proposed demodulator has been evaluated by link-level simulations in EDGE systems. The numerical results show that the system performance can be significantly improved comparing to the conventional hard-bit and soft-bit demodulators.