Ravinder David Koilpillai

Equalizer performance with diversity for U.S. digital cellular

In mobile communications, the receiver must mitigate severe signal impairments arising from multipath and Rayleigh fading. Multipath produces intersymbol interference (ISI), necessitating the use of an equalizer in the receiver. The performance of the equalizer can be significantly improved using antenna diversity, thereby allowing the use of lower C/I values. This C/I reduction offers potential for capacity enhancement. This paper describes the use of pre-detection antenna diversity in conjunction with a MLSE receiver for the U.S. Digital Cellular (USDC) system. It is shown that the receiver meets all the USDC (IS-54) performance specifications with a significant margin and has a computational complexity of less than 4 MIPS.<<ETX>>

A new family of modulation schemes for land mobile radio

Achievable spectral efficiency in land-mobile radio (LMR) systems is limited by adjacent-channel interference (ACI) specifications. Spectral efficiency can be improved by using digital modulation schemes. With linear modulation schemes, intermodulation products produced by non-linear power amplifiers lead to increased ACI. In this paper, a new family of linear modulation schemes called envelope-constrained modulation schemes is introduced to improve the spectral efficiency of LMR systems using quasilinear power amplifiers. These modulation schemes exhibit low envelope variations and thus ease the linearity requirements on the power amplifier. Also, power savings can be realized by incorporating coded modulation. An analytical evaluation of the performance is performed to illustrate the gain achievable using the new modulation schemes.