Noncoherent NEC assisted detection of QAM in mobile radio

Cellular systems are characterized both by a great subscriber base and very limited frequency spectrum resources. Techniques such as frequency reuse, directional antennas, advanced speech and channel coding, power control etc. have been studied and proposed as solutions to increase the capacity. Modulations other than binary (GMSK) and quaternary (π/4-DQPSK) have not been widely adopted until lately. The most important reasons for this are the low signal-to-noise ratios encountered in the macrocells and the multipath fading, which may prove completely destructive for the signal. The receiver is consequently obstructed from recovering reliable amplitude and phase references resulting in irreducible error rates for highly efficient modulations such as QAM. With this paper, we attempt to introduce star QAM properly encoded at the transmitter. In addition, the adaptation of the star QAM to the requirements of the NEC receivers, already tested with MPSK modulations, opens new areas of applications that need higher efficiency. The performance improvement derived from Monte-Carlo simulations is a strong indication of what it is going to follow in the area