Raymond Toy

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>>

Converting call-by-reference to call-by-value: Fortran and Lisp coexisting

Programs written in languages supporting call-by-reference continue to be of interest in functional programming circumstances where call-by-value is standard. In particular, if we can find a neat interface, by converting Fortran to Lisp we allow programmers to take advantage of an interactive functional symbolic system while running legacy numerical code. We show this can be done without unacceptable loss of efficiency. In building a combined symbolic-numeric environment such a conversion and combination may increase the synergy between the two approaches to scientific computing. This paper builds upon earlier reported work on f2cl.

Interference simulations for a home base station system

This paper presents the results for interference simulations for the GSM-based home base station (HBS) system for a high-density urban scenario. In one possible HBS system, the HBS system is not frequency-coordinated with the overlaying macro cellular network. This paper investigates the impact of such a system on the macro cellular network by simulating the interference environment seen by both the macro cellular system and the HBS system. These simulations study the interference as a function of the HBS base station power and of the traffic load in the HBS system. The results show that such HBS systems can coexist with macro systems in high-density urban areas without producing noticeable interference to the macro cellular system and that the HBS system has good performance.

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.