Clayton Okino

A network architecture for precision formation flying using the IEEE 802.11 MAC protocol

Precision formation flying (PFF) missions involve the tracking and maintenance of spacecraft in a desired geometric configuration. Autonomous control of the distributed spacecraft requires inter-spacecraft communications with guaranteed performance. We present a network architecture that supports PFF control across the various phases of mission operations, ranging from initial random deployment to precision formation. The architecture incorporates the IEEE 802.11 MAC protocol and utilizes both its distributed control function (DCF) and point coordination function (PCF) modes as appropriate to the PFF operational phase. A proactive routing protocol provides timely topology status. A new application layer protocol is incorporated which provides a simple interface between the PFF control application and the underlying communications network

Communications architecture for space-based sensor networks

Numerous planned and proposed future space exploration missions employ multiple spacecraft that perform multipoint sensing. Distributed space-based sensing missions can significantly benefit from incorporation of cross-link communications capabilities, thereby forming space-based networks, by enabling continuous access to any/all spacecraft via a single ground contact, real-time coordinated observations, and autonomous in situ processing within a spatial neighborhood of spacecraft. We present a communications architecture for space-based sensor networks. Because of the large inter-spacecraft distances, directional antennas are used, with a single half-duplex transceiver per spacecraft to achieve low cost. Orbital motion induces a dynamic albeit predictable geometry (and topology) among the spacecraft. Primary offered traffic is sensor telemetry destined to the Earth ground station, although other traffic patterns are also treated. We present a technique that derives the link activation schedule (transmit/receive mode and communications neighbor selection) and routes used for efficient traffic relay through the network, leveraging the Florens and McEliece algorithm for tree networks. An illustrative example is presented, and throughput and latency performance are evaluated. An extension to the networking method is described that is traffic adaptive.

On the diameter of sensor networks

In space exploration, cooperative modulation techniques have been proposed for prolonging the life-time of sensor nodes within a multihop network. The desire to efficiently reduce the overall energy-per-bit of a node motivated this study on the hop diameter (synonymous to the number of hops in a path) of sensor networks. In this study, we analysed and found that when the number of transmissions are bounded by constants /spl les/ 20, the likelihood of successful broadcast is small. Using simulations, we observed that the diameter decreases very fast as the transmission radius increases. Another observation is that the largest connected component emerges when the transmission radius reaches 0.3/spl radic/A, where A is the area containing the nodes. This may be used to determine the ideal amplification, although further simulations on larger networks could be helpful. We also found a large gap between the number of nodes required to populate the area, when all the nodes must be connected, or when only 90% of the nodes are connected.

Space-Based Voice over IP Networks

In human space exploration missions, there will be a need to provide voice communications services. In this work we focus on the performance of Voice over IP (VoIP) techniques applied to space networks, where long range latencies, simplex links, and significant bit error rates occur. Link layer and network layer overhead issues are examined. We posit that imposing additional speech processing latencies in the form of multiple frames per packet is tolerable in the space regime, and show resulting performance overhead improvements. Furthermore, we find that even with channel bit error rates of 10-5 and 10-4, the frame size does not severely degrade the original speech.

An advanced orbiting systems approach to quality of service in space-based intelligent communication networks

As humans and robotic technologies are deployed in future constellation systems, differing traffic services will arise, e.g., realtime and non-realtime. In order to provide a quality of service framework that would allow humans and robotic technologies to interoperate over a wide and dynamic range of interactions, a method of classifying data as realtime or non-realtime is needed. In this paper, we present an approach that leverages the Consultative Committee for Space Data Systems (CCSDS) Advanced Orbiting Systems (AOS) data link protocol. Specifically, we redefine the AOS Transfer Frame Replay Flag in order to provide an automated store-and-forward approach on a per service basis for use in the next-generation interplanetary Internet. In addition to addressing the problem of intermittent connectivity and associated services, we propose a follow-on methodology for prioritizing data through further modification of the AOS transfer frame

Space-based autonomous reconfigurable protocol chip

In this paper, we present an architecture for a reconfigurable protocol chip for space-based applications. We present a model for examining various stimuli for reconfiguration in space, and identify some approaches to operating on the stimuli. In particular, we examine fault tolerant schemes and reconfiguration based on detection of a link layer framing format

A reliable data transfer architecture for a space-based reconfigurable protocol chip

In this paper, we present an architecture for reliable data transfers for space-based applications. In particular, we examine a network interface card (NIC) architecture, a reliable link layer approach based on hybrid automatic-repeat-request (ARQ) scheme, and then consider the corresponding handshaking associated with file transfers. We present results on the performance of our methodology and an implementation strategy for incorporation of the mechanism into a reconfigurable protocol chip architecture

Intelligibility and Space-based Voice with Relaxed Delay Constraints

In this paper, we leverage the long range end-to-end scenarios envisioned for lunar and beyond voice conversations by allowing non-traditional additional processing delay for quasi-real-time voice conversations. The concept of improving the quality of end-to-end voice conversations for long delay environments is considered by utilizing Luby transforms on the conjugate-structure algebraic-code-excited linear-prediction (CS-ACELP) codec. In addition, this paper also examines the use of automated speech recognition software as a means of generating a quantifiable metric for speech intelligibility in the spirit of the diagnostic rhyme test (DRT).

Performance Evaluation of Video Codecs in the Space Environment

In human missions to other planets and natural satellites (e.g., return to the Moon and future missions to Mars), there will be a need to provide video services for such functions as monitoring analysis, personal private video conversations and general public outreach. There is a desire to provide these services by leveraging terrestrial Internet concepts and technology. In this work we focus on the video performance mechanisms as they are impacted in a space environment where long range latencies and bit errors arise in the wireless/RF links. We provide results from experiments using open source implementations of commercial video standards. Both Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity (SSIM) are used as a performance metrics.

Adaptive source and channel coding for distributed applications

Distributed applications are often faced with a choice between improved throughput or improved reliability but not both. We argue that this is not a strict dichotomy and propose a framework that improves both application performance and reliability by adaptively adjusting source and channel coding parameters. For simplicity, we assume that the source and channel we work with are memoryless and in general behave in a way such that Shannons separation theorem holds. Although not all sources and channels could be characterized as such, doing so allows us to work this resource allocation problem in parallel. We reduce redundant transmissions and minimize bandwidth utilization through an LZ77 style dictionary based source coding approach. To ensure data integrity, we apply rateless forward error correction techniques at the transport layer. Our algorithm works in conjunction with physical layer forward error correction and generates just enough overhead needed to achieve error free transmission without requiring a heavy use of a reverse channel for acknowledgments. We show through simulations that our combined source and channel approach reduces network traffic in our experimental platform by a measurable amount while maintaining and at times exceeding the Quality of Service (QoS) that is obtained without our technique. 1 2