Combinatorial pulse position modulation for power-efficient free-space laser communications

A new modulation technique called combinatorial pulse position modulation (CPPM) is presented as a power-efficient alternative to quaternary pulse position modulation (QPPM) for direct-detection, free-space laser communications. The special case of 16C4PPM is compared to QPPM in terms of data throughput and bit error rate (BER) performance for similar laser power and pulse duty cycle requirements. The increased throughput from CPPM enables the use of forward error corrective (FEC) encoding for a net decrease in the amount of laser power required for a given data throughput compared to uncoded QPPM. A specific, practical case of coded CPPM is shown to reduce the amount of power required to transmit and receive a given data sequence by at least 4.7 dB. Hardware techniques for maximum likelihood detection and symbol timing recovery are presented

Combinatorial FSK modulation for power-efficient high-rate communications

Deep-space and satellite communications systems must be capable of conveying high-rate data accurately with low transmitter power, often through dispersive channels. A class of noncoherent Combinatorial Frequency Shift Keying (CFSK) modulation schemes is investigated which address these needs. The bit error rate performance of this class of modulation formats is analyzed and compared to the more traditional modulation types. Candidate modulator, demodulator, and digital signal processing (DSP) hardware structures are examined in detail. System-level issues are also discussed

Planar Approximation for the Least Reliable Bit Log-Likelihood Ratio of 8-PSK Modulation

The optimum decoding of component codes in block coded modulation (BCM) schemes requires the use of the log-likelihood ratio (LLR) as the signal metric. An approximation to the LLR for the least reliable bit (LRB) in an 8-PSK modulation based on planar equations with fixed-point arithmetic is developed that is both accurate and easily realisable for practical BCM schemes. Through an error power analysis and an example simulation it is shown that the approximation results in less than 0.06 dB in degradation over the exact expression at an Es/N0 of 10 dB. It is also shown that the approximation can be realised in combinatorial logic using roughly 7300 transistors. This compares favourably to a look-up table approach in typical systems

Power, Propulsion, and Communications for Microspacecraft Missions

The development of small sized, low weight spacecraft should lead to reduced scientific mission costs by lowering fabrication and launch costs. An order of magnitude reduction in spacecraft size can be obtained by miniaturizing components. Additional reductions in spacecraft weight, size, and cost can be obtained by utilizing the synergy that exists between different spacecraft systems. The state-of-the-art of three major systems, spacecraft power, propulsion, and communications is discussed. Potential strategies to exploit the synergy between these systems and/or the payload are identified. Benefits of several of these synergies are discussed

Practical 8-PSK Block-Coded Modulation With Convolutional Codes and Soft Decision Block Codes for Packet Networks

The design and performance of a class of practical rate 2/3, 8-PSK block-coded modulation (BCM) (also referred to as multilevel modulation codes) schemes are presented. These BCM schemes utilise both convolutional codes and block codes, and have block lengths that are matched with relatively short packet lengths to satisfy requirements in packet-wireless networks. Decoding issues such as optimum signal metrics and soft-decision decoding of block codes are addressed. The performance is evaluated and simulated. It is found that these BCM schemes exhibit a coding gain comparable to 16, 32 and 64 state Ungerboeck (1982) TCM codes, but require less complexity to decode