Deep Space Optical Communications Research Articles

Performance Analysis of Gradual Multi-pulse Pulse-Position Modulation in Deep-Space Optical Communications

A gradual multi-pulse pulse-position modulation (gradual MPPM) scheme is proposed as a new modulation scheme to improve both the performance and bandwidth-utilization efficiency of the conventional optical multi-pulse pulse-position modulation (MPPM) scheme in deep-space optical communications. Whereas in the conventional MPPM scheme, a fixed number of optical pulses is transmitted in every signal block, a variable number of pulses are transmitted in the proposed scheme. Information is represented by different combinations of the positions of these pulses. The transmission characteristics, bandwidth utilization, and power requirements for the proposed scheme are studied in this paper. Several performance measures are derived and compared with those of the conventional MPPM scheme in deep-space optical communications. Our results reveal that, at the same average power, the proposed gradual MPPM scheme achieves much lower levels of symbol-error rates than those of the ordinary MPPM scheme, whereas, at the same peak power levels, the ordinary MPPM outperforms the gradual scheme. Also, in terms of bandwidth-utilization efficiency, the proposed modulation scheme achieves higher efficiency than the ordinary MPPM by allowing many more symbols to be transmitted per frame.

A Kalman filter based synchronization scheme for telescope array receivers in deep-space optical communication links

In this paper, the impact of random synchronization errors on the performance of ground-based telescope array receivers for an inter-planetary optical deep-space communication (ODSC) link is investigated. An adaptive method based on Kalman filters is developed for the synchronization and combination of different telescope signals in the array. An end-to-end simulation platform for ODSC link between Earth and planet Mars is implemented that incorporates pulse-position modulation (PPM), direct-detection array receivers, and photon-counting detectors. The effects of atmospheric turbulence and background noise are also modeled. The performance of array receivers is evaluated in terms of probability of symbol error and achievable data rates. The simulation results show that the Kalman filter-based synchronization scheme keeps the synchronization induced power losses to less than 1dB. The analysis also shows that in the worst-case operational scenario and presence of random synchronization errors, an array consisting of hundred, 1m telescopes performs almost similar to a single 10m telescope. Hence, the degradation in the combined signal due to synchronization errors places a minor limitation on the number of telescopes in a telescope array receiver consisting of up to 100 telescope elements.

SPC-APPM coded modulation for deep-space optical communications

A coded modulation scheme for deep-space optical communications is proposed, which is composed of an outer single-parity-check (SPC)-based product code, an interleaver, a bit-accumulator and a pulse-position modulation (PPM). It is referred as SPC-APPM code, which is decoded with an iterative demodulator-decoder using standard turbo-decoding techniques. Investigations show that the scheme has the advantages of low encoding and decoding complexities, good performance and flexible code rate for all rates above 1/2. Meanwhile, simulation results demonstrate that the SPC-APPM provides the performance similar to the low-density parity-check-APPM (LDPC-APPM), superior to the LDPC-PPM and product accumulate code-PPM (PA-PPM), although inferior to serially concatenated PPM (SCPPM). At the bit error rate (BER) of 10−5, the performance of SPC-APPM is about 0.7 dB better than LDPC-PPM and 1.2 dB better than PA-PPM.

Feasibility of infrared Earth tracking for deep-space optical communications

Infrared (IR) Earth thermal tracking is a viable option for optical communications to distant planet and outer-planetary missions. However, blurring due to finite receiver aperture size distorts IR Earth images in the presence of Earth's nonuniform thermal emission and limits its applicability. We demonstrate a deconvolution algorithm that can overcome this limitation and reduce the error from blurring to a negligible level. The algorithm is applied successfully to Earth thermal images taken by the Mars Odyssey spacecraft. With the solution to this critical issue, IR Earth tracking is established as a viable means for distant planet and outer-planetary optical communications.

Deep-Space Optical Communications: Future Perspectives and Applications

The concept of deep-space optical communications was formulated shortly after the invention of lasers. The promise of laser communications, high data rate delivery with significantly reduced aperture size for the flight terminal, led to the pursuit of several successful experiments from Earth orbit and provided the incentive for further demonstrations to extend the range to deep space. This paper is aimed at presenting an overview of the current status of optical communications with an emphasis on deep space. Future perspectives and applications of optical communications related to near-Earth and interplanetary communications are also addressed.

Multidimensional Pulse-Position Coded-Modulation for Deep-Space Optical Communication

In order to achieve multigigabit transmission (projected for 2020) for the use in interplanetary communications, in this letter, we propose the use of multidimensional pulse-position modulation (PPM). From Shannon's theory, we know that information capacity is a logarithmic function of signal-to-noise ratio, but a linear function of number of dimensions. By using pulse-positions as a basis function, we can improve the spectral efficiency of conventional PPM. The N-dimensional PPM (ND-PPM) can, therefore, be used to solve the high-bandwidth requirements of future deep-space optical communications. The N -dimensional signal constellation can be obtained as N-dimensional Cartesian product one-dimensional pulse-amplitude modulation constellation. The improvement of ND-PPM over PPM for N=8 in strong turbulence regime is even 3.21 dB at a bit-error rate (BER) of 10-5. In addition, the spectral efficiency of the proposed scheme is N/log2N times better than that of PPM.

EXIT Function Aided Design of Iteratively Decodable Codes for the Poisson PPM Channel

This paper presents and compares two iterative coded modulation techniques for deep-space optical communications using pulse-position modulation (PPM). The first code, denoted by SCPPM, consists of the serial concatenation of an outer convolutional code, an interleaver, a bit accumulator, and PPM. The second code, denoted by LDPC-PPM, consists of the serial concatenation of an LDPC code and PPM. We employ Extrinsic Information Transfer (EXIT) charts for their analysis and design. Under conditions typical of a communications link from Mars to Earth, SCPPM is 1 dB away from capacity, while LDPC-PPM is 1.4 dB away from capacity, at a Bit Error Rate (BER) of approximately 10-5. However, LDPC-PPM lends itself naturally to low latency parallel processing in contrast to SCPPM.

Diversity Reception for Deep-Space Optical Communication Using Linear Projections

A novel spatial diversity receiver for deep-space optical communication links is proposed. Using digital micromirror devices, the receiver optically computes linear projections of the turbulence-degraded focal-plane signal distribution onto an orthogonal binary basis. By using such projections, an estimate of the signal distribution is computed and updated adaptively to follow the time variations of the signal distribution. The estimate is used to perform selection combining, i.e., to select the portions of the focal plane that contain significant energy for symbol detection. The proposed receiver is less complex, requires less high-speed analog electronics and has lower preamplifier noise than a comparable multiple-detector array receiver. On the other hand, the proposed receiver requires more optical components and additional digital hardware to control the micromirror devices. Symbol error-rates (SERs) are simulated on a photon-counting channel and performance improvements about 2-5 optical decibels (dBo) over a conventional single-detector receiver are obtained at SER = 10-2.

A Novel Turbo Coded Modulation Scheme for Deep Space Optical Communications

A novel turbo coded modulation scheme, called the turbo-APPM, for deep space optical communications is proposed. The proposed turbo-APPM is a serial concatenation of turbo codes, an accumulator and a pulse position modulation (PPM), where turbo codes act as an outer code while the accumulator and the PPM act together as an inner code. The generator polynomial and the puncturing rule for generating turbo codes are chosen to lower the bit error rate. At the receiver, the joint iterative decoding is performed between the inner decoder and the outer turbo decoder. In the outer decoder, local iterative decoding for turbo codes is conducted. Simulation results are presented showing that the proposed turbo-APPM outperforms all previously proposed schemes such as LDPC-APPM, RS-PPM and SCPPM reported in the literature.

LDPC-Coded $M$-ary PSK Optical Coherent State Quantum Communication

This paper addresses two important problems of interest for deep-space optical communications, quantum inter-chip/intra-chip optical communications and quantum-key distribution: 1) the problem of coded <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary phase-shift keying optical coherent-state quantum communication in the absence of background radiation, and 2) the problem of coded binary coherent state communication in the presence of background radiation. In both cases large girth low-density parity-check (LDPC) codes are used as channel codes. With girth-10 LDPC-code of rate 0.8 and BPSK, the bit-error ratio of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> can be achieved for average number of signal photons of 0.73, resulting in net-effective coding gain of 7.63 dB.

Effect of Atmospheric Turbulence on AcquisitionTime of Ground to Deep Space Optical Communication System

Effect of Atmospheric Turbulence on AcquisitionTime of Ground to Deep Space Optical Communication System

Optimizations of a Hardware Decoder for Deep-Space Optical Communications

The National Aeronautics and Space Administration has developed a capacity approaching modulation and coding scheme that comprises a serial concatenation of an inner accumulate pulse-position modulation (PPM) and an outer convolutional code [or serially concatenated PPM (SCPPM)] for deep-space optical communications. Decoding of this code uses the turbo principle. However, due to the nonbinary property of SCPPM, a straightforward application of classical turbo decoding is very inefficient. Here, we present various optimizations applicable in hardware implementation of the SCPPM decoder. More specifically, we feature a Super Gamma computation to efficiently handle parallel trellis edges, a pipeline-friendly ;maxstar top-2; circuit that reduces the max-only approximation penalty, a low-latency cyclic redundancy check circuit for window-based decoders, and a high-speed algorithmic polynomial interleaver that leads to memory savings. Using the featured optimizations, we implement a 6.72 megabits-per-second (Mbps) SCPPM decoder on a single field-programmable gate array (FPGA). Compared to the current data rate of 256 kilobits per second from Mars, the SCPPM coded scheme represents a throughput increase of more than twenty-six fold. Extension to a 50-Mbps decoder on a board with multiple FPGAs follows naturally. We show through hardware simulations that the SCPPM coded system can operate within 1 dB of the Shannon capacity at nominal operating conditions.

A Coded Modulation Scheme for Deep-Space Optical Communications

A coded modulation scheme for deep-space optical communications is studied, which is a serial concatenation of an outer low-density parity-check (LDPC) code, an interleaver, a bit-accumulator, and pulse-position modulation (PPM). It is referred as LDPC-APPM. It is decoded with an iterative demodulator-decoder using standard turbo-decoding techniques. Simulation results show that the LDPC-APPM with an outer LDPC code of medium code length suffers a loss of about 0.7 dB at a bit-error rate of relative to the serially concatenated PPM (SCPPM) of similar parameters, which consists of the serial concatenation of an outer convolutional code, an interleaver, a bit-accumulator, and PPM; however, it has better code rate flexibility especially for high rates and simpler implementation structure than SCPPM. Further, it can achieve better performance than the LDPC-PPM of the same rate and length, which consists of the serial concatenation of an LDPC code and PPM.

Analysis for Mars Laser Communications System in USA

空间光通信因其体积小、质量轻、数据率高,已经得到世界各国的普遍重视,尤其是进地卫星光通信系统的在轨实验的成功,使人们建立起用激光进行深空通信的信心,而我国的深空光通信技术起步较晚,因此在深空光通信系统的设计,元器件的选用方面有必要参考国外的深空光通信系统,因此本文对美国最新研制的火星激光通信演示系统(MLCD)进行全面分析,重点分析了该系统跟瞄(PAT)子系统,通信子系统,地面接收端的工作原理和工作方式,对系统中采用的新器件、新技术进行了详细的分析,在此基础上,对该系统的可靠性和可行性进行了分析,给出了未来深空激光通信技术研究的发展方向,为我国将来开展深空光通信的研究提供参考.

Yb-doped fiber amplifier for deep-space optical communications

A custom-developed high-power laser based on a Yb-doped amplifier is characterized as a transmitter for deep-space optical communications. The key requirements are high peak power at moderate data rates with good beam quality. The transient pulse dynamics are modeled via a simple rate equation approach and reveal a qualitative agreement with the pulsed performance. Peak powers were obtained up to 8 kW for a 22-ns pulsewidth at a 3.5-kHz repetition rates. The peak power dropped significantly as the repetition rate was increased to 50 kHz.

Performance Analysis and Tradeoffs for Dual-Pulse PPM on Optical Communication Channels With Direct Detection

The performance and tradeoffs of multipulse position modulation (MPPM) are investigated and compared with that of the traditional (single) pulse position modulation (PPM) scheme typically employed on the optical direct-detection channel. While the primary motivation for the consideration of the problem is to provide performance improvement for deep-space optical communications where narrow high-peak-power transmitted pulses offer significant advantages in terms of detection probabilities and background suppression capabilities at the receiver, the results obtained are sufficiently generic as to apply to other applications.

Capacity of the low-photon-rate direct-detection optical pulse-position-modulation channel in the presence of noise photons

We derive expressions for the capacity of the pulse-position-modulated (PPM) direct-detection photon-counting channel in the presence of noise photons in addition to the signal-dependent shot noise that is normally considered in studying photon counting at low photon rates. We note that even a small mean number of noise photons per PPM count bin significantly decreases the capacity of the channel. These results are useful for comparisons of performance that are obtained by use of real coding and synchronization algorithms with photon-counting PPM schemes that are currently being considered for deep-space optical communications.

Stability analysis of direct-detection cooperative optical beam tracking

The system under consideration is a cooperative spatial tracking system between two stations for laser beam communications, using a quadrant photodetector at each station. After determining the equilibrium points of the cooperative system for the case of periodical relative motion, the authors concentrate on the stability of the transient behavior around the equilibrium points for the case of uniform angular relative motion. This case corresponds to an assumption that the steady-state motion is slow with respect to transient phenomena, and is applicable to currently foreseen intersatellite and deep-space optical communications. The analysis is aimed at determining the combined effect of the basic system parameters, such as propagation delay time, tracking loop gains, DC servomotors time constant, and point-ahead velocity error, on the stability and the transient behavior of the overall tracking system. The stability conditions and the transient response around the steady-state trajectory provide a tool for evaluating the consistency of the design parameters for a given propagation delay. >

Space instrumentation for laser communications

Deep space optical communications link, fabricating operational prototype of flight hardware for spaceborne terminal