Spectrally Efficient FDM over Satellite Systems with Advanced Interference Cancellation

For high data rates satellite systems, where multiple carriers are frequency division multiplexed with a slight overlap, the overall spectral efficiency is limited. This work applies highly overlapped carriers for satellite broadcast and broadband scenarios to achieve higher spectral efficiency. Spectrally efficient frequency division multiplexing (SEFDM) compresses subcarrier spacing to increase the spectral efficiency at the expense of orthogonality violation. SEFDM systems performance degrades compared to orthogonal signals, unless efficient interference cancellation is used. Turbo equalisation with interference cancellation is implemented to improve receiver performance for variable coding, compression and modulation/constellation proposals that may be applied in satellite communications settings. Such parameters may be set to satisfy pre-defined spectral efficiency values for a given quality index (QI) or associated application. Assuming LDPC coded data, the work proposes two approaches to receiver design; a simple matched filter approach and an approach utilising an iterative interference cancellation structure specially designed for SEFDM. Mathematical models and simulations studies are presented indicating promising gains to be achieved for SEFDM transmission with advanced transceiver architectures at the cost of increased complexity at the receiver

Generalised model for prediction and synthesis of negative capacitance at microwave frequencies using common-gate MESFET

Newly-derived equations describing the input impedance of MESFET common-gate stages are presented, allowing the synthesis of negative input capacitance using a simple MESFET circuit. Results derived from such equations show excellent agreement with those obtained using a microwave simulator, up to frequencies close to the cut-off frequency of the MESFET employed. A three-stage optical receiver front-end is used as an illustrative example to show the generation of negative capacitance under practical circuit constraints. © 1996 IEEE

Performance of a noncoherent decoder for spectral amplitude‐coding electronic‐code

The performance of a noncoherent decoder based on a pair of distributed‐based transversal filters architecture is reported. Analysis based on experimental results validates the decoder as a proof‐of‐concept using microwave integrated circuits. Front‐end transversal filters are designed with large degree of freedom to generate and correlate temporal phase‐coded signals. Receiving functions are aligned with slots of spectrally encoded channels to make available spectral amplitude‐coding electronic‐code division multiple access. Noncoherent ultra‐wideband receiver concepts are applied to model the decoder synchronized to shot noise pulse trains. The despreading operation involves capturing sufficient amount of energy to demodulate matched and unmatched users. Electronic transversal filters implemented with a suitable number of taps allow bipolar detection of concurrent users whereas the noncoherent reception of energy of sub‐bands is fundamental to achieve orthogonality among channels, as we show in this article

Extending Distributed-Based Transversal Filter Method to Spectral Amplitude Encoded CDMA

In this paper, the analog code modulation characteristics of distributed-based transversal filters (DTFs) suitable for use in spectrally encoded CDMA systems are presented. The DTF is verified as an appropriate method to use in high-speed CDMA systems as opposed to previously proposed methods, which are intended for Direct Sequence (DS) CDMA systems. The large degree of freedom of DTF design permits controlling the filter pulse response to generate well specified temporal phase-coded signals. A decoder structure that performs bipolar detection of user subbands giving rise to a Spectral-Amplitude Encoded CDMA system is considered. Practical implementations require truncating the spreading signals by a time window of duration equal to the span time of the tapped delay line. Filter functions are chosen to demodulate the matched channel and achieve improved user interference rejection avoiding the need for transversal filters featuring a large number of taps. As a proof-of-concept of the electronic SAE scheme, practical circuit designs are developed at low speeds (3-dB point at 1 GHz) demonstrating the viability of the proposal