⚡ electrical engineering

Multi-/Uni-Cast Non-Orthogonal Multiple Access-Based INAC

This paper proposes a novel Multi-/Uni-Cast Non-Orthogonal Multiple Access-based Integrated Navigation and Communication (INAC) signal structure that shares a common pseudo-noise sequence between navigation and communication services, deriving closed-form performance expressions to demonstrate that prioritizing power for the multi-cast signal (MO-INAC) significantly enhances positioning accuracy and bit error rate performance, particularly for MEO satellites.

Original authors: Yaoyu Zhang, Xin Sun, Tianwei Hou, Anna Li, Sofie Pollin, Yuanwei Liu, Arumugam Nallanathan

Published 2026-05-27

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CC BY 4.0

Original authors: Yaoyu Zhang, Xin Sun, Tianwei Hou, Anna Li, Sofie Pollin, Yuanwei Liu, Arumugam Nallanathan

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine a satellite orbiting Earth as a busy radio station. Traditionally, this station has to choose: either broadcast a navigation signal (like a lighthouse beam telling ships where they are) OR broadcast a communication signal (like a podcast for phones). If it does both, it usually has to take turns, switching back and forth very quickly. This is like a lighthouse that turns off its beam every time it wants to shout a message; the ships get confused, and the signal gets weaker.

This paper proposes a clever new way to do things called MUC-NOMA-based INAC. Here is the simple breakdown of what they did and found:

The Core Idea: The "Shared Highway"

Instead of taking turns (Time Division) or using different lanes (Frequency Division), the researchers put the navigation signal and the communication signal on the same road at the same time.

Think of it like a heavy truck (Navigation) and a fast sports car (Communication) driving side-by-side on the same single-lane highway.

The Truck (Navigation): Needs to be steady and reliable so ships can find their way. It carries a "Multi-cast" message (one message for everyone).
The Car (Communication): Needs to go fast to send data. It carries a "Uni-cast" message (a specific message for one person).

The Problem: The "Traffic Jam"

If you put a fast car and a slow truck on the same road, they crash into each other (interference). The fast car might get blocked by the truck, or the truck might get jostled by the car.

The Solution: The "Smart Receiver" (SIC)

The paper suggests a special receiver (the person listening to the radio) that uses a technique called Successive Interference Cancellation (SIC). Imagine the receiver is a very smart listener who knows the rules of the road:

Step 1: The listener first tunes into the loudest signal. If the truck is louder, they listen to the truck first, decode the navigation message, and then "subtract" the truck's noise from their ears.
Step 2: Once the truck is gone from their mind, the quiet sports car becomes clear, and they can decode the communication message.
Step 3 (The Reverse): If the car is louder, they listen to the car first, subtract it, and then hear the truck.

The Two Scenarios: Who Gets the "Loud" Spot?

The researchers tested two different ways to share the power (volume) between the truck and the car:

MO-INAC (Multi-cast Oriented): The Navigation Signal (Truck) gets the most power.
- Result: The navigation signal is super clear and accurate. The communication signal is a bit weaker but still works. This is great for MEO satellites (Medium Earth Orbit) where you need precise positioning.
UO-INAC (Uni-cast Oriented): The Communication Signal (Car) gets the most power.
- Result: The communication is very fast and clear. However, because the car is so loud, it creates more "noise" for the truck. The navigation signal has to work harder to be heard, which can slightly reduce its accuracy.

Key Findings (The "Takeaways")

Speed vs. Accuracy: There is a trade-off. If you try to send communication data faster (make the car go faster), the navigation accuracy (how well the truck stays on the road) goes down.
Power Matters: Giving more power to the navigation signal makes the positioning much better. Giving more power to the communication signal makes the data transmission better.
Better than the Old Way: Compared to the old method of taking turns (TDMA), this new "sharing the road" method is more efficient. It uses less power and gets more done, even though it's a bit more complex to decode.
The Sweet Spot: For Medium Earth Orbit satellites, the MO-INAC approach (prioritizing the navigation signal) turned out to be the best balance, offering excellent positioning accuracy while still allowing for decent communication.

In a Nutshell

The paper introduces a new signal structure that lets satellites send navigation and communication data simultaneously on the same frequency without them ruining each other. By using a "smart listener" that cancels out interference, they proved that you can get high-precision navigation and reliable communication at the same time, provided you carefully balance how much "volume" (power) you give to each signal.

Technical Summary: Multi-/Uni-Cast Non-Orthogonal Multiple Access-Based INAC

Problem Statement
The rapid development of satellite communication and navigation has created an urgent need to integrate these technologies within a single system to achieve reliable communication and precise navigation simultaneously. Traditional approaches, such as time-division, frequency-division, or code-division multiplexing, suffer from inherent inefficiencies. Time-division multiplexing (TDM) causes discontinuity in navigation signals, hindering signal capture and degrading ranging performance. Frequency-division multiplexing (FDM) consumes substantial bandwidth, while code-division multiplexing (CDM) is constrained by the limited number of available spreading sequences. Furthermore, existing Integrated Navigation and Communication (INAC) studies often lack comprehensive signal-level performance analysis, particularly regarding Bit Error Rate (BER) and positioning accuracy under Non-Orthogonal Multiple Access (NOMA) frameworks. While NOMA has been proposed for INAC, practical solutions for interference elimination and detailed performance characterization across different power allocation strategies remain unexplored.

Methodology
The authors propose a novel signal structure based on Multi-/Uni-Cast Non-Orthogonal Multiple Access (MUC-NOMA). In this architecture, navigation and communication signals share a common pseudo-noise (PN) sequence at the signal level. The system divides the communication signal into two parts: a portion ( $\xi$ ) is merged with the navigation signal to form a low-rate multi-cast signal, while the remainder ( $1-\xi$ ) is transmitted as a high-rate uni-cast signal. These two streams are superimposed using NOMA techniques.

Two distinct operating scenarios are defined based on power allocation factors ( $\beta_1$ for multi-cast, $\beta_2$ for uni-cast, where $\beta_1 + \beta_2 = 1$ ):

Multi-Cast-Oriented (MO-INAC): More power is assigned to the multi-cast signal ( $\beta_1 > \beta_2$ ).
Uni-Cast-Oriented (UO-INAC): More power is assigned to the uni-cast signal ( $\beta_1 < \beta_2$ ).

To mitigate co-channel interference, the receiver employs Successive Interference Cancellation (SIC). The signal processing algorithm decodes the higher-power signal first, reconstructs it, subtracts it from the received signal, and then decodes the lower-power signal. The paper develops a unified theoretical framework to derive closed-form expressions for the BER of both navigation and communication signals, as well as the ranging accuracy (positioning error). The analysis accounts for the rate-split nature of the DSSS structure, where the number of uni-cast symbols superimposed within one multi-cast symbol ( $M$ ) fundamentally alters interference behavior.

Key Contributions

Signal Architecture: The paper proposes a MUC-NOMA-based INAC signal where low-rate multi-cast and high-rate uni-cast signals are superimposed over the same PN sequence. This allows navigation and communication to share time, frequency, and code resources at the bit level within a Direct Sequence Spread Spectrum (DSSS) framework.
Unified Theoretical Framework: The authors derive exact closed-form BER expressions for both MO-INAC and UO-INAC scenarios. Unlike conventional NOMA systems assuming identical symbol rates, this work addresses the rate-split DSSS structure, deriving despread decision statistics, probability density functions (PDFs), and BER expressions that account for distinct error propagation mechanisms in each scenario.
Ranging Accuracy Analysis: The study analytically maps residual interference to delay-locked loop (DLL) tracking jitter, providing closed-form expressions for ranging accuracy. It explicitly links ranging performance to communication data rates and power allocation.
High-SNR Approximations: Approximate closed-form BER expressions are derived for high Signal-to-Noise Ratio (SNR) conditions, revealing fundamental relationships between system performance, power allocation factors, and communication rates.

Results
Numerical evaluations and Monte Carlo simulations (using MEO satellite parameters) confirm the analytical results:

MO-INAC Performance: In the MO-INAC scenario, assigning more power to the multi-cast signal yields excellent positioning and BER performance for the navigation signal. However, as the communication data rate increases, the BER of the communication signal increases while the navigation signal's BER decreases.
UO-INAC Performance: In the UO-INAC scenario, assigning more power to the uni-cast signal reduces interference in shared resources. When the communication power allocation is high and the data rate is low, both signals exhibit good BER performance. However, higher communication data rates lead to reduced ranging accuracy due to limited coherent integration time.
Trade-offs: A trade-off exists between the BER of the communication signal and the navigation signal. In MO-INAC, increasing the navigation power allocation improves navigation BER but degrades communication BER. In UO-INAC, increasing communication power improves communication BER but can degrade navigation performance due to error propagation from the SIC process.
Comparison with Baselines: Compared to Time-Division Multiple Access (TDMA) and Cyclic Code Shift Keying (CCSK) baselines, the proposed NOMA scheme offers superior resource utilization and scalability. While TDMA and CCSK may offer slightly better navigation BER in specific isolation, the NOMA scheme avoids the resource scarcity of CDM and the integration time loss of TDM, while maintaining compatibility with legacy receivers by preserving the original PN phase.
Ranging: The MO-INAC scenario demonstrates superior ranging performance compared to UO-INAC and pure navigation baselines in certain conditions, as the superposition of communication bits can provide energy gains or self-interference cancellation. Conversely, UO-INAC ranging accuracy degrades as communication data rates increase.

Significance and Claims
The paper claims that the proposed MUC-NOMA-based INAC signal structure provides a practical solution for integrating satellite communication and navigation, overcoming the discontinuity issues of TDM and the resource inefficiency of FDM/CDM. By providing closed-form analytical expressions, the work offers a comprehensive framework for evaluating system performance without relying solely on simulations. The authors assert that the MO-INAC scenario is particularly resilient to path loss and signal degradation, making it a preferred option for Medium Earth Orbit (MEO) satellite systems. The study highlights that while there are performance trade-offs between communication and navigation services depending on power allocation and data rates, the proposed architecture enables flexible resource splitting to balance these requirements, ultimately improving system efficiency and reliability.