This paper prcscnts an all digital US-CDMA upstream trailsmittcr. and a head-eml bascband recciwr for upstream cnlde/HFC networks. The upstrcam transmitter supports freit,y of t,hc carrier, QPSK and QAM constellat,ions A\I: variable symhol lat,cs from ltiUkchip/s to S.l2h~lchip/s incrcasing by power of i,rol and direct-digital iq-convcrsiion to achieve a~~u r a t~) arnplitnde and pilase of moduIatiw1. The trnnsnritter connist,s of pulse shaping tilt,er; half-band filter, ciiscadcd intcgrator-comb (CIC) filter-. and iiiverse SINC fillcr. The all digital ~~~~~~~~end hascband reccivcr snpport,s prug~ammable rltiadrnt,urc amplit tide modulntim up t,o (;4QAhl. Fast, t,iming and carrier recovery algorithms a r adoptcd for hnrst, inodc transmission Cudc acquisit,ion can bc iic1iievt.d wit,lrin 2 syiiibols: and tlrc carrier acqtiisitim CAN lie achicicd wit,hin 31 symbols. All digil al 1.iiiiiiig recovery is designed with ~21101,prn syrnhol t i n -ilOOppiri of carrier frcqrieiicy offset.
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In an OFDMA network, the downlink power spectral density (PSD) is varying dynamically to support multiple access, it is quite difficult to obtain the instantaneous interference PSD through either measurements or signaling. In this paper, we evaluate the impact of unknown non-flat interference in OFDMA system. We compare the performance of three different receiver algorithms under the effect of unknown non-flat interference PSD for AWGN and fading channel. We prove that there is a significant performance lose if we don't know the exactly interference PSD in some case. We will demonstrate the effect of interference under several factors, including SIR, the loading factor and Dmin of receiver codeword.978-1-4244-1688-2/08/$25.00 c 2008 IEEE
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