A new group demodulator employing multi-symbol chirp Fourier transform

Abstract

T1ii.r p a p e r l m p m s U g i m p denrodrrlntor that ernploys multisymbol chirp Fourier iruiisji)rni io deinodulate pulse shuppd unci bit nsj~nchronous sigriols: this is not possible witli coriveiitioriul ~~O L I~J denioduluiois based on chirp Foitrirr tmi.$orni. Moreover, n iiovel clock iiniirig rstiriintioii sc.lrenie for the p o j~o s e d groirp deniodirlator is p1.oposed. The clock tirniiig is estinratedfi.onr the phase of two frequency coriijwirirts of tlre p~raniblr sigrial wid1 a siniple calculation. Computer siniirlatioii r~esults show that the iotul bit rrror rate degradutiori of the pvoposetl group deniodiilator einploying 7-symbol chirp Fourier trunsform is less tlian 0.3dB ot BER=IO.J even rvlieii roof Nyquist (@=OS) ,filtrr.ed nsynchroi~oi4s FDMA signals are received. Introd~ictioiiIn digital mobile and personal communication systems, the base stations tnust handle many frequency division multiple access (FDMA) signals simultaneously. To demodulate such signals, the group deinodulator [ 1][2][3][4][5] is one powerful solution to minimize the hardware size of the base stations. Conventional group demodulators can be divided into two categories. One is based on group frequency converting using the fast Fourier transform (FFT) algorithm [3][4], and the other utilizes the frequency division multiples -time division multiples (FDM-TDM) conversion using chirp Fourier transform [ 1][2]. The group demodulator based on chirp Fourier transform (CFT group demodulator) has advantages in hardware size and maximum operarion speed to handle a number of channels.Conventional CFT group demodulators, however, have two major problems. First, the modulation signals must be square pulse signals instead of pulse shaped and band-limited signals and carriers must be spaced by multiples of the Nyquist frequency. This Nyquist-spaced square pulse transmission cannot be used for commercial systems because its out of band radiation is significant and frequency allocation flexibility is quite poor. If a conventional CFT group demodulator processes band-limited signals, considerable bit error rate degradation arises from the adjacent channel interference (ACI), the inter symbol interference (13) and decreased eye aperture, as will be described in the following section. Second, the symbol timing phase of each FDMA signal must be synchronized with the sweep tiinhg phase of the chirp signal at the receiver input. Therefore an accurate timing control loop is required. Due to these problems, conventional CFT group demodulators have not been employed in existing mobile or personal communication systems.To solve these problems, this paper proposes a group demodulator based on mnlti-symbol chirp Fourier transform. By using more than one symbol for chirp Fourier transform and some additional signal processing operations, the proposed group demodulator can demodulate pulse shaped and time asynchronous signals with negligibly small degradation. 2.'Conventional CFT group demodulatorA block diagram of a conventional CFT group dernodulator ...

A new group demodulator with multi-symbol chirp Fourier transform for mobile communication systems

“…1. The timing difference AT can be determined with a simple symbol timing detection scheme [6]. This scheme detects the timing offset between the symbol timing and the chirp sweep timing with the phases of two specified frequency components of the preamble signals.…”

“…Conventional CFT group demodulators, however, have two major problems [6]. First, the modulation signals must be square pulse signals not band-limited signals, and the carriers must be spaced by multiples of the Nyquist frequency (reciprocal of the symbol duration).…”

“…To solve the above two problems, the group demodulator employing the multi-symbol chirp Fourier transform has been proposed [6]. However, this group demodulator has not taken AI1 into account.…”