OTFS: A New Generation of Modulation Addressing the Challenges of 5G(1)

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.
摘要表达了以下几个意思

1. OTFS的定义：在一种称为延迟-多普勒表示的信号表示中，将信息QAM符号多路复用到与局部脉冲相对应的新型载波波形上
2. 实现方式：将时频选择性信道变成了不变，分离，正交的相互作用
3. 达到的效果：所有的QAM符号经历了相同的衰落，时延多普勒分集分支进行了相干组合，能够在多普勒和多径信道条件下，以MIMO阶和鲁棒性对频谱效率进行线性缩放，以达到最佳性能-复杂性折衷的信道容量
4. 应用：结合了雷达和通信，产生高分辨率的图像，实现MU-MIMO的增益

OTFS- A Next Generation Modulation

Problem, the reason why communication make progress

• CDMA: have limited flexibility for adaptation and inferior achievable throughput
• OFDM:
  1. MU MIMO, the cost of very complex architectures that cannot practically achieve capacity, suffers performance degradation in the presence of time and frequency selectivity
  2. non-trivial dynamic channel conditions, adaptation becomes realistic

Design Philosophy

fuse together two contradictory principles – (1) the principle of spreading (as used in CDMA) to obtain resilience to narrowband interference and to exploit channel diversity gain for increased reliability under unpredictable channel conditions and (2) the principle of orthogonality (as used in OFDM) to simplify the channel coupling for achieving higher spectral densities with a superior performance-complexity tradeoff

OTFS combines the reliability and robustness of spread spectrum with the high spectral efficiency and low complexity of narrowband transmission

OTFS in core 5G use cases

1. eMBB: OTFS enables scaling of spectral efficiency with increased MIMO order under any channel condition with optimal performance-complexity tradeoff
2. Internet of Things (IoT). maximizes the link budget (energy per bit) and minimizes the number of retransmissions under power and latency constraints. low PAPR and maximum available duration (to maximize link budget) while extracting full time-frequency diversity (to minimize number of retransmissions).
3. Communication under high mobility conditions V2V or HST. maximizes throughput, reliability, and performance consistency
4. Ultra-Reliable Low Latency Communication (URLLC). exhibits resilience to narrowband interference
5. mm-Wave communication:explain how phase noise can be mitigated