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Survey of Inter-satellite Communication for Small Satellite Systems: Physical Layer to Network Layer View
Radhika Radhakrishnan, William Edmonson, Fatemeh Afghah, R. Rodriguez-Osorio, Frank Pinto, Scott Burleigh
TL;DR
Small satellite networks need inter-satellite communications to support autonomous, dynamic missions despite spacecraft resource constraints. This paper surveys inter-satellite communication research through the OSI model, reviews the first three layers, and identifies design parameters and proposed solutions for multiple missions.
Problem
Autonomous networks of heterogeneous small satellites require communication among spacecraft while operating under size, mass, power, and dynamic-topology constraints.
Method
The paper surveys inter-satellite communication research using the OSI model and reviews design parameters for the physical, data link, and network layers.
Results
The survey compiles design parameters, proposed solutions to small-satellite communication challenges, and examples of formation-flying missions.
Takeaways & Limitations
Inter-satellite communication research supports future heterogeneous space networks requiring higher data rates, minimal latency, and diverse mission capabilities.
Takeaways & Limitations
SDR-based inter-satellite networks remain exposed to malicious software, signal interception, external interference, and evolving cryptanalysis threats.
Abstract
from arXiv · showhide
Small satellite systems enable whole new class of missions for navigation, communications, remote sensing and scientific research for both civilian and military purposes. As individual spacecraft are limited by the size, mass and power constraints, mass-produced small satellites in large constellations or clusters could be useful in many science missions such as gravity mapping, tracking of forest fires, finding water resources, etc. Constellation of satellites provide improved spatial and temporal resolution of the target. Small satellite constellations contribute innovative applications by replacing a single asset with several very capable spacecraft which opens the door to new applications. With increasing levels of autonomy, there will be a need for remote communication networks to enable communication between spacecraft. These space based networks will need to configure and maintain dynamic routes, manage intermediate nodes, and reconfigure themselves to achieve mission objectives. Hence, inter-satellite communication is a key aspect when satellites fly in formation. In this paper, we present the various researches being conducted in the small satellite community for implementing inter-satellite communications based on the Open System Interconnection (OSI) model. This paper also reviews the various design parameters applicable to the first three layers of the OSI model, i.e., physical, data link and network layer. Based on the survey, we also present a comprehensive list of design parameters useful for achieving inter-satellite communications for multiple small satellite missions. Specific topics include proposed solutions for some of the challenges faced by small satellite systems, enabling operations using a network of small satellites, and some examples of small satellite missions involving formation flying aspects.
1 Introduction
Small satellites offer lower-cost, faster-to-develop platforms for coordinated missions, but their constrained resources and dynamic environments require inter-satellite communication networks. This survey organizes research and mission examples around the OSI framework, emphasizing the first three layers.
- Small satellite systems: Small satellites are classified by mass into mini-, micro-, nano-, pico-, and femto-satellite classes, typically below 500 kg.
- Motivation for inter-satellite communications: Networks of heterogeneous small satellites can support coordinated measurements with improved spatial and temporal resolution and reduced human intervention.
- Survey scope and framework: The survey reviews inter-satellite communication research from 2000–2015 using the OSI model, focusing on physical, data link, and network layers.
- Operational challenges: Dynamic or unpredictable space environments can disrupt links, while centralized systems may require a new master satellite after failure.
- Distributed spacecraft architectures: Distributed processing and fractionated spacecraft use multiple communicating components or processors, with architectures such as star, ring, linear bus, hybrid, and layered designs.
- Mission examples: Formation-flying missions reviewed include GRACE, ESSAIM, PRISMA, and ELISA, covering scientific, military, rendezvous, and transmitter-mapping applications.
2 Background
Small satellites can operate in trailing, cluster, or constellation formations within distributed space systems, where inter-satellite communication supports autonomous, coordinated networked missions.
- Satellite Formation Flying: The three common formation types are trailing or leader-follower, cluster, and constellation.Trailing spacecraft share an orbit; clusters remain closer in separate orbits; constellations use multiple orbital planes.
- Satellite Formation Flying: Trailing formations place multiple spacecraft in the same orbit at specified separations.
- Satellite Formation Flying: Cluster formations deploy satellites in respective orbits that remain close together and cover a smaller portion of Earth.
- Satellite Formation Flying: Constellations organize satellites across orbital planes, with each plane containing enough satellites to provide required service coverage.
- Inter-Satellite Communications: Distributed Space Systems use networked spacecraft for autonomous data transfer and functions including distributed processing, servicing, proximity operations, and fractionated operations.The surveyed literature addresses these systems through an OSI-based communication architecture, focusing on generally characterizable lower layers.
3 Design of Various Layers of the OSI Model
The survey frames small-satellite inter-satellite communication through the OSI model, including an architecture that can merge upper-layer functions and a detailed focus on lower-layer design.
- OSI-Based Architecture: The OSI model provides a reference framework for organizing communication between devices in a small-satellite network.For small-satellite systems, upper-layer functionalities may be merged and implemented using software programs.
3.1 OSI Physical Layer
The physical layer defines the hardware means for transmitting raw data bits across a network and specifies fundamental transmission parameters.
- Physical Layer: The physical layer transmits raw data bits over a hardware medium rather than logical data packets.Its parameters include electrical connectors, transmission media, modulation schemes, and transmission frequency.
3.1.1 Frequency allocation and data rate
Physical-layer frequency and data-rate design must match mission traffic, network architecture, link conditions, and small-satellite resource constraints.
- Frequency Allocation and Data Rate: Required bandwidth depends on mission objectives, transmitted data type and amount, transmission frequency, and inter-satellite-link statistics.Existing allocated spectrum was considered sufficient for expected demands through 2020.
- Frequency Allocation and Data Rate: Channel capacity can increase through bandwidth or signal-to-noise-ratio changes, using modulation, coding, antenna gain, transmitter power, or reduced system temperature.The available options are constrained by small-satellite hardware and power limits.
- Frequency Allocation and Data Rate: Maximum supported data rate determines the required bandwidth for different small-satellite configurations.
- Frequency Allocation and Data Rate: Bandwidth categories are narrow (< 100 Kbps), medium (100 Kbps to 10 Mbps), and wide (> 10 Mbps).
- Frequency Allocation and Data Rate: The data-rate formulation accounts for bandwidth category, network architecture, mission bandwidth probability, simultaneous cross-link count, and maximum data rates by data type.A surveyed interplanetary rate-control protocol adapts to available bandwidth and uses Tornado codes for packet-level forward error correction.
- Frequency Allocation and Data Rate: Interference depends on concurrent transmitters, satellite spatial distribution, antenna design, and operating periods.Multiple-access techniques and directional antennas can increase the number of simultaneously operated cross-links.
- Frequency Allocation and Data Rate: Inter-satellite frequencies from VHF (30 MHz) to Ka band (40 GHz) are feasible when satellites have sufficient power for transmission and reception.Most CubeSat programs use UHF/VHF transceivers for downlink communication without inter-satellite links.
3.1.2 Modulation and coding schemes
The survey compares modulation and coding choices for small-satellite inter-satellite links, emphasizing power, throughput, bandwidth efficiency, and robustness trade-offs.
- BPSK is preferred because coherent systems require the least power for a given throughput and bit error rate.BPSK introduces receiver delay while coherently locking to the incoming signal.
- QPSK and offset-QPSK can provide approximately twice the bandwidth efficiency of BPSK.Channel-induced phase distortion can degrade performance and may be addressed using differential PSK.
- Higher-order PSK improves spectral efficiency but requires extra power because closely spaced symbols are more vulnerable to noise and distortion.
- Forward error correction adds parity bits so receivers can detect and correct a limited number of noise- or interference-induced bit errors.The cited passage identifies convolutional coding with Viterbi decoding as a common scheme.
3.1.3 Link design
Link design analysis evaluates whether an inter-satellite communication system can meet mission requirements, balancing performance, cost, and reliability across the complete link and payload.
- Link-budget analysis relates transmitted and received power to assess system feasibility and trade off performance, cost, and communication-link reliability.
- Design begins by identifying mission requirements, including satellite count, orbital parameters, objectives, and ground- or relay-station locations.
- Inter-satellite, uplink, and downlink data rates depend on sampling, quantization, bits per symbol, mission objectives, exchanged data, transmission frequency, and available bandwidth.
- Each link is designed using frequency band, modulation and coding, antenna characteristics, interference, atmospheric or rain absorption, transmitter power, and received noise.
- Communication-payload sizing depends on antenna configuration, antenna mass and power, transmitter mass and power, payload mass and power, and transmission or reception power.
3.1.4 Antenna design in small satellites for inter-satellite links
Antenna design for small-satellite inter-satellite links must reconcile coverage, steering, range, bandwidth, power, mass, and platform constraints through isolated antennas, arrays, or combined concepts.
- Broad-beam isolated antennas offer compact, simple architectures, whereas antenna arrays provide beam steering and higher gain.
- The GAMANET antenna system uses one 2.45 GHz S-band patch per CubeSat face and combines up to three weighted antenna signals.Simulations found beam-forming control performed better than antenna selection.
- Free-drifting OLFAR satellites vary in distance and orientation, making links in arbitrary directions difficult; single-patch designs trade path loss against antenna size and limit range.The OLFAR spacecraft are 3U CubeSats measuring 10×10×30 cm.
- Antenna specifications must be established early because communications, spacecraft-platform, and mission requirements constrain formation-flying designs.
- Mission and platform constraints: Small-satellite antenna requirements include a 40 deg steering margin, unknown-formation-position support, space-environment survivability, low cost, external attachment, broad scanning, attitude-independent polarization, and compact construction.
- Subsystem constraints: Subsystem design must balance light planar construction, a 10 cm square CubeSat aperture, solar-panel area, modularity, frequency-band losses, range, gain, bandwidth, and duplex operation.Modular apertures can accommodate changing inter-satellite distance or transfer rate.
- Antenna concepts: The two proposed concepts are orthogonal-face individual antennas with selection or beam forming, and a steerable single-face array with a narrower, higher-gain beam.Combining arrays on three faces can reduce available solar-cell area unless deployable solar cells are used.
3.2 OSI Data Link Layer
The data link layer coordinates shared-medium access, reliability, and traffic performance in satellite networks, with protocols adapted to mission topology, scale, contention, and resource limits.
- The data link layer handles framing, addressing, synchronization, error and flow control, and multiple access through logical-link-control and MAC sublayers.
- Scalability and adaptability: MAC protocols must adapt when satellites join, fail, or reorganize into different topologies.
- MAC design must account for channel utilization, latency, throughput, fairness, mission type, topology, satellite count, power, computing resources, and adaptability.
- Contention-based protocols let satellites compete for a channel and resolve collisions, whereas conflict-free protocols avoid contention through predetermined access rules.
- Multiple-access protocols: Optimized IEEE 802.11 inter-frame spacing can maintain constant throughput, while adaptive contention windows and smart antennas improve operation over longer links.The proposed smart-antenna integration increases protection against fading, thermal noise, and multiple-access interference.
- Multiple-access protocols: Directional CSMA/CA/RTS/CTS can save power in formation patterns such as leader-follower systems, but is intended for missions without tight communication links.
- Multiple-access protocols: LDMA combines CSMA under low contention with TDMA under high contention, achieving higher throughput than either protocol and lower collision probability than pure CSMA.Its scalability is limited because CSMA degrades with network size and TDMA scheduling may not cover large networks.
3.3 OSI Network Layer
The network layer addresses routing and connectivity in dynamic small-satellite networks, including intermittent links and changing topology. Surveyed approaches include metric-based routing, specialized discovery protocols, adaptive algorithms, and Delay-Tolerant Networking.
- Routing metrics: Routing protocols select paths using metrics such as delay, bandwidth, reliability, link status, load, and hop count.Transmission power and time are highlighted as key optimization objectives; multi-hop transmission can reduce communication power.
- Routing schemes: Small-satellite routing choices depend on mission requirements, topology, and whether network control is distributed or centralized.Proactive schemes maintain complete topology knowledge, while reactive schemes discover routes as needed.
- Routing protocols: Proposed small-satellite network-layer protocols include neighbor discovery, synchronization, decentralized routing, node affiliation, and packet forwarding.Neighbor Discovery Protocol is investigated in detail in the cited work.
- Dynamic routing: Dynamic routing methods address topology changes through handover optimization, topology slices, clustering, and hybrid static-dynamic routing.The surveyed approaches include Globalstar-based routing, cluster-based MANET routing, and virtual-topology ATM routing.
- Delay-Tolerant Networking: Delay-Tolerant Networking retains data during temporary link outages and forwards it when communication opportunities return, unlike TCP/IP packet discard during partitions.DTN can use orbital predictions and ground-station locations to construct uploadable contact plans.
- Delay-Tolerant Networking: DTN has been demonstrated in several spaceflight contexts and may improve relay performance, but small satellites constrain its processing, storage, and power resources.The surveyed text reports increased relay data rates in simulations and identifies deployment constraints on small spacecraft.
4 Proposed Inter-Satellite Communication Solutions for Small Satellite Systems
The paper surveys and proposes physical- and data-link-layer solutions for small-satellite inter-satellite communication, emphasizing software-defined radios, antenna systems, and formation-flying links. Reported designs support adaptable networking and demonstrated synchronization, ranging, and data-link performance, while retaining substantial resource, pointing, interference, and security constraints.
- Proposed solutions: The proposed solutions address selected physical- and data-link-layer challenges in implementing inter-satellite communications for small-satellite systems.The section presents solutions based on the research group's expertise.
- Software-defined radio: Software-defined radios implement baseband functionality in software, enabling flexible communication without the hardware constraints of fixed radio architectures.The surveyed SDR functions include demodulation, channel coding, source coding, and adaptable waveform processing.
- Software-defined radio: SDR inter-satellite links can support resource sharing, relative-position, time, and frequency synchronization, ad-hoc links, and reduced ground traffic.The SWIFT SDR platform has achieved high-speed data links above 10 Mbps.
- Software-defined radio: SDR flexibility supports cognitive and adaptive operation, multimode operation, radio reconfiguration, remote upgrades, and new services without hardware changes.A single radio can accommodate different bit rates, waveforms, modulation schemes, and error-correction schemes.
- SDR constraints: SDR implementation must reserve memory, processing, and power resources for future waveforms and mission-time reconfiguration, increasing demands on the satellite bus.The cited design discussion specifically identifies memory, CPU/FPGA processing, and DC power capability.
- SDR challenges: SDR security risks include unauthorized malicious software installation, unintended signal reception, and external interference.Suggested protections include cryptographic algorithms and digitally signed certificates.
- SDR and antenna challenges: Increasing downlink rates expose limitations of low-directivity antennas, interference, and reliance on spacecraft attitude control for fixed-beam pointing.Electronically steered arrays of low-directivity elements are presented as a better solution.
- Demonstrated systems: SWIFT-RelNav provides better-than-10 cm relative ranging, 12 Mbps crosslink data rates, a 10^-6 bit error rate, and synchronization better than 1 ns and 0.1 ppb.The platform combines relative range and attitude determination with inter-satellite communications.
4.3 Optimum MAC Protocols for Inter-Satellite Communication for Small Satellite Systems
The section evaluates MAC and routing approaches for leader-follower, cluster, and constellation formations under small-satellite constraints. It compares modified CSMA/CA/RTS/CTS with a hybrid TDMA/CDMA protocol using simulation-based performance measures.
- The proposed MAC design considers mission objective, topology, satellite count, limited power, and limited computing resources.
- Modified CSMA/CA/RTS/CTS protocol: Modified CSMA/CA/RTS/CTS uses distributed coordination and reactive on-demand routing for leader-follower, cluster, and constellation formations.
- Modified CSMA/CA/RTS/CTS protocol: 24% maximum throughput is achieved for leader-follower and constellation formations, compared with 11% for cluster formation.
- Modified CSMA/CA/RTS/CTS protocol: The CSMA/CA/RTS/CTS protocol does not require strict synchronization but is suitable only for missions that tolerate communication delays.
- Hybrid TDMA/CDMA protocol: The hybrid TDMA/CDMA protocol combines collision-free TDMA allocation with simultaneous DS-CDMA transmission for clustered heterogeneous satellites.
- Hybrid TDMA/CDMA protocol: 95% throughput is reported for hybrid TDMA/CDMA, whose delays remain nearly constant as traffic increases, unlike CSMA/CA/RTS/CTS.
- Hybrid TDMA/CDMA protocol: The hybrid protocol supports scalable clustered networks and can use TDMA-centric or CDMA-centric framing for variable or relatively consistent packet sizes.
5 Design Parameters for Inter-Satellite Communication Design Process
The design process derives OSI-layer specifications from mission-dependent constraints, including topology, data exchange, bandwidth, timing, processing, scalability, connectivity, and data size. These parameters affect protocol choices across network architectures and applications.
- Inter-satellite communication specifications are derived from design constraints determined by satellite behavior in different constellation types.
- Network topology: Network topology may be fixed or variable, and topology changes affect application software, transport parameters, and network-layer routing metrics.
- Data transmission: Missions exchange science, navigation, health/status, and command/control data at frequencies determined by mission requirements.
- Bandwidth and data size: Bandwidth requirements depend largely on mission type and data-transmission frequency, while variable data sizes require adaptive protocols.
- Real-time access: Real-time applications such as servicing and proximity operations require communication-channel access with minimal packet delay.
- Processing capabilities: Centralized systems may assign greater processing capability to a mother satellite, whereas purely distributed networks use comparable satellite capabilities.
- Reconfigurability and scalability: Reconfigurability and scalability require protocols to detect node failures or additions and maintain mission objectives across network architectures.
- Connectivity: Intermittent connectivity makes terrestrial protocols unsuitable without modification and makes routing a major challenge for space applications.
6 Future Research Directions
Future research emphasizes robust ad-hoc networking for large satellite populations with dynamic topology and high data rates. Autonomous agent-based computing is proposed to support situation-dependent satellite decisions.
- Future space networks require coordination of satellite timing, position, and spacing through advanced channel-access and routing methods.
- Agent-based platforms are proposed so satellites can receive neighboring information and decide actions autonomously rather than relying on manual scheduling from Earth.
7 Conclusions
The survey reviews inter-satellite communication design issues across the OSI model for heterogeneous small-satellite networks. It covers physical-layer, MAC, routing, DTN, mission, and system-parameter research, while identifying solutions and directions for future missions.
- The survey studies inter-satellite communication design issues using the OSI model, with emphasis on the last three layers.
- It reviews modulation, coding, links, antennas, software-defined radio, MAC protocols, routing schemes, and DTN for small-satellite networks.
- The paper demonstrates software-defined radio, modular antenna arrays, feasible multiple-access protocols, formation-flying missions, and a set of design parameters.