OTFS: A New Generation of Modulation Addressing the Challenges of 5G (1802.02623v1)

Abstract: In this paper, we introduce a new 2D modulation scheme referred to as OTFS (Orthogonal Time Frequency & Space) that multiplexes information QAM symbols over new class of carrier waveforms that correspond to localized pulses in a signal representation called the delay-Doppler representation. OTFS constitutes a far reaching generalization of conventional time and frequency modulations such as TDM and FDM and, from a broader perspective, it establishes a conceptual link between Radar and communication. The OTFS waveforms couple with the wireless channel in a way that directly captures the underlying physics, yielding a high-resolution delay-Doppler Radar image of the constituent reflectors. As a result, the time-frequency selective channel is converted into an invariant, separable and orthogonal interaction, where all received QAM symbols experience the same localized impairment and all the delay-Doppler diversity branches are coherently combined. The high resolution delay-Doppler separation of the reflectors enables OTFS to approach channel capacity with optimal performance-complexity tradeoff through linear scaling of spectral efficiency with the MIMO order and robustness to Doppler and multipath channel conditions. OTFS is an enabler for realizing the full promise of MUMIMO gains even in challenging 5G deployment settings where adaptation is unrealistic.

• The paper proposes a novel OTFS modulation scheme that utilizes delay-Doppler representation to achieve uniform channel impairments and improved MIMO performance.
• It demonstrates significant performance gains, including up to 53% throughput improvement in high-order MIMO systems and energy savings of up to 8 dB in IoT scenarios.
• The paper highlights OTFS’s adaptability to high mobility and URLLC conditions, paving the way for its integration into evolving 5G and mm-Wave communications.

Overview of OTFS: A New Generation of Modulation for 5G Challenges

The paper presents a detailed exploration of the Orthogonal Time Frequency & Space (OTFS) modulation scheme as a novel approach to address challenges inherent in 5G network deployment. Unlike conventional Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM), OTFS operates in a delay-Doppler representation. This method allows for the multiplexing of Quadrature Amplitude Modulation (QAM) symbols over carrier waveforms that are localized in both domains. Such a design is a significant conceptual advancement, aligning radar principles with wireless communication to achieve high-resolution delay-Doppler imaging of channel reflectors.

Core Modulation Characteristics

OTFS introduces a new paradigm of modulation that is both invariant and orthogonal across delay-Doppler impairments. By interacting optimally with wireless reflectors, OTFS processes the channel into an invariant, separable interaction whereby the impairments experienced by transmitted symbols remain uniform, and diversity branches are effectively combined. This structure offers significant advantages for MIMO systems in terms of spectral efficiency, particularly in scenarios where adaptation to channel conditions might not be feasible.

Performance Analysis in Key 5G Use Cases

The paper analyzes the OTFS modulation scheme across several core 5G use cases to highlight performance gains over conventional OFDM systems:

1. Enhanced Mobile Broadband (eMBB): OTFS demonstrates superior spectral efficiency and a better performance-complexity tradeoff, particularly for high-order MIMO systems. Through simplified equalization and precoding processes, OTFS offers a noticeable gain in throughput and reliability, with comparative studies showing up to 53% improvement in certain MIMO setups.
2. Internet of Things (IoT): The OTFS transmission mode optimizes for energy efficiency by maximizing the link budget and reducing retransmissions, with specific configurations allowing for a decrease in transmission power required by up to 8 dB compared to traditional SC-FDMA schemes.
3. High Mobility (V2V, HST): The modulation scheme adapts to high Doppler spread environments, such as those faced in vehicle-to-vehicle communication, by utilizing Doppler as a diversity source and minimizing the adverse effects of inter-carrier interference (ICI).
4. Ultra-Reliable Low Latency Communication (URLLC): OTFS exhibits robustness against narrowband interference, ensuring stable performance even when integrating URLLC packets, as the symplectic Fourier transform disperses interference across the delay-Doppler grid.
5. mm-Wave Communication: The potential of OTFS is explored for mm-Wave deployments, where it offers a solution to significant phase noise and propagation challenges by eliminating the need for a cyclic prefix and efficiently mitigating ICI.

Technical and Theoretical Implications

From a theoretical perspective, OTFS modulation provides an elegant solution for translating spectral gains from radar advancements into communication systems. By leveraging its delay-Doppler framework, it outpaces traditional methods in handling highly dynamic 5G environments, thereby offering a robust platform for evolving wireless requirements.

Future Prospects

Looking forward, the adoption of OTFS in real-world 5G infrastructure could advocate for the modulation's integration into more complex network scenarios, including adaptations for evolving spectrum usage and further exploration into its utility for beamforming applications.

In conclusion, OTFS stands as a promising modulation technology that elegantly addresses 5G challenges through its innovative design and practical advantages in performance-heavy network conditions.