IEE Colloquium on Advanced Modulation and Coding Techniques for Satellite Communications

TRL Technology Ltd have, over the past 2 years, been under contract to INMARSAT to produce a combined modem, capable of operating as any of the three modem types within the system, in order to verify the INMARSAT-M System Definition Manual (SDM); the specification. TRL's involvement has centred on all aspects of the modem(s). The authors summarise the main problem areas for the modem(s) and give s... View full abstract»

The authors review optical technologies for space communications. Initially the advantages of this technology are described and the tradeoffs between direct detection and coherent detection explained. As a model for deep space communications, the ideal photon counting channel is used and it is illustrated that the most efficient modulation format is pulse position modulation (PPM). They go on to c... View full abstract»

The requirement of a carrier synchronisation system to track the significant Doppler frequency shift of a transmission from a low Earth orbit (LEO) satellite has been investigated. The performances of two frequency estimator structures have been compared in the presence of the time-varying Doppler shift characteristic of the transmission from a LEO satellite and AWGN. The frequency detector derive... View full abstract»

Over the past two decades, many new methods of modulating a signal with digital signals have been proposed. The author reviews some of these methods: sinusoidal MSK; multi-amplitude MSK; Ungerboeck coded modulation; multi-h coded modulation; tamed frequency modulation; CPM; quadrature overlapped raised-cosine modulation; cross correlated PSK; correlative PSK; and digital phase modulation View full abstract»

It is well known that digital modulation systems of the QAM family exhibit cyclostationary behaviour, which makes symbol timing recovery (STR) possible from a signal which has no discrete spectral component at the symbol rate. The literature on the subject, however, describes only algorithms which operate in the time domain. The authors try to show that a frequency domain analysis brings out the e... View full abstract»

The authors discuss the maximum rate at which data can be reliably communicated through an AWGN channel where phase only modulation is used, and the reduction of the maximum rate if the demodulator in the system responds only to the phase of the modulated signal. They then look at how these rates are reduced if the modulator is restricted to a finite set of phase symbols (such as in 8 or 16-PSK sy... View full abstract»

One important difference between a satellite channel and an additive white Gaussian noise (AWGN) channel is the nonlinear characteristic of the power amplifiers used. Mobile systems are often power limited at the mobile Earth station, high bit rate TDMA are often power limited at the satellite, and in both cases the power efficient amplifiers used introduce nonlinear distortion. Theoretical analys... View full abstract»

The following topics were dealt with: Q²PSK data aided carrier recovery and clock recovery; symbol timing recovery; low Earth orbit satellite frequency detectors; satellite mobile radio modems; channel capacity; nonlinear channel performance degradation; 8-ary PSK modulation; and optical links. View full abstract»

An investigation of a new power and bandwidth efficient modulation scheme (Q2PSK) has been conducted, to evaluate new synchronization procedures and digital implementation of a Q2PSK transmitter-receiver (Tx-Rx) system. The authors present new data aided (DA) carrier phase and timing synchronization algorithms for Q2PSK signals, and compare it with an alternative m... View full abstract»

The authors discuss the possibility of transmitting synchronous digital hierarchy (SDH) signals through two-link nonlinear satellite channels. Transmitting such high bit rate signals using the standard 72 MHz transponder bandwidth requires the use of high level modulation schemes. The techniques and technologies needed to make the use of 8-ary PSK transmission feasible for future satellite communi... View full abstract»