We present a new joint symbol timing and carrier frequency offset estimation algorithm for noncoherent orthogonal continuous-phase M-ary frequency-shift keying (M-CPFSK). Our algorithm performs nondata-aided feedforward processing of finite-length observations, and it is suited for an all-digital modem implementation based on a DSP or an ASIC processor. The algorithm exploits phase continuity of M-CPFSK in order to generate both a spectral component at the carrier frequency offset and a timing error signal. This is obtained without nonlinear transformations of the received signal involving noise/spl times/noise products. Thus, our algorithm can operate at a very low input signal-to-noise ratio. We discuss the operating range of our algorithm, and we show that no additional overhead (training sequence) in excess of the standard overhead of FDMA/TDMA packet transmission is required to resolve timing and frequency ambiguities. Moreover, we show that by differentially preceding the transmitted symbols, it is possible to eliminate automatically frequency ambiguities, at the price of a slight increase in the bit-error rate. An approximate mean-square error analysis of the estimators and simulation results prove that our algorithm provides good performance, even with a relatively short observation block length and large carrier frequency offset. Computer simulations show also that our algorithm is extremely robust to phase noise. These features make our algorithm a good candidate for satellite FDMA/TDMA applications in the 20-30 GHz band, with a large number of users and bursty transmission.

The concept of digital direct satellite broadcasting (D-DBS), which allows unprecedented flexibility by providing a large number of audio-visual services, is introduced. The concept assumes an information rate of about 40 Mb/s, which is compatible with practically all present-day transponders. After discussion of the general system concept, the optimization procedure is introduced, and results of the transmission system optimization are presented. Channel distortion and uplink/downlink interference effects are taken into account by means of a time domain system computer simulation approach. It is shown, by means of link budget analysis, how a medium-power direct-to-home TV satellite can provide multimedia services to users equipped with small (60-cm) dish antennas.>

Recent trends in digital communications are opening commercial applications to code division multiple access (CDMA). A novel access technique based on bandlimited quasi-synchronous CDMA (BLQS-CDMA) is described, showing all the advantages of synchronizing conventional direct sequence CDMA to drastically reduce the effect of self-noise. Bandlimitation is achieved with no detection loss by means of Nyquist chip shaping, leading to a simple all-digital demodulator structure. Detection losses due to imperfect carrier frequency and chip timing synchronization are analytically derived and numerical results are checked by computer simulations. Impairments due to satellite transponder distortions are evaluated. The full digital modem structure is presented, together with possible applications to mobile and very small aperture terminal (VSAT) satellite communications.>