Orthogonal Time Frequency Space (OTFS) is a new multiple access scheme that is now being discussed in the cellular market and becoming a contender for 6G. Orthogonal Frequency Division Multiplexing (OFDM) is well established in the industry and the scheme used in 4G and 5G, but it has its limitations, including poor performance in high-speed wireless scenarios and high energy consumption. OTFS promises overcoming high energy consumption, supports very high-speed communication scenarios, and delivers higher spectral efficiency by reducing high Cyclic Prefix (CP). Nevertheless, commercialization initiatives to productize OTFS faces two key challenges: OTFS technology has the promise to overcome high energy consumption but there is still no product in the market that uses OTFS’s energy reducing capability to reduce energy consumption of the network; and only one product in the market for increasing the spectral efficiency using OTFS. Also, OTFS and the delay-doppler channel estimation algorithm that is behind it have not been developed by Tier-One Telecom Equipment Manufacturers (TEMs), which may be a commercial barrier for the new protocol in the industry. Nevertheless, according to ABI Research market insights, all Tier-One TEMs are now accelerating their OTFS research towards 6G.
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OTFS Supports Communications at High Speed, Delivers Higher Spectral Efficiency and Engery Efficiency
OFDM as a modulation technique is not fit-for-purpose for 6G as it has two major limitations:
- Unsuitability for communication at very high speed: OFDM is unsuitable for critical communications at very high speeds. When transmitter and receiver are moving in high speed, time variation of the channel degrades the orthogonality of different sub-carriers, leading to leakage of power among orthogonal subcarriers. This is known as Inter-Carrier Interference (ICI) and is the main reason behind signal degradation in OFDM, which is a challenge in high-speed mobility scenarios.
- High power consumption: Handling very large Peak-to-Average Power Ratios (PAPRs) is one of the fundamental engineering problems in the Radio Frequency (RF) portion of OFDM modems. OFDM Power Amplifiers (PAs) are oversized and their power efficiency is drastically reduced. These power inefficiencies due to high PA power consumption, in turn, make OFDM modulation technique less power efficient suitable for power-challenged applications, including sensor-type communications. This lack of energy efficiency of OFDM will become a major problem in 6G where the Internet of Things (IoT) is a foundational component for new use cases and applications.
OFDM is a digital modulation method of multi-carrier variety which modulates data in the Time-Frequency (TF) domain. In contrast, OTFS is a two-dimensional modulation technique that modulates data in Delay Doppler domain. Time and frequency are orthogonal or vertical to each other in OTFS waveform. OTFS modulation technique combines two amplitude modulation signals into a single channel and, in turn, helps double the effective bandwidth of the resulting channel. This higher effective bandwidth leads to higher data transfer rate, essential for 6G use cases in near future. Also, Cyclic Prefix (CP) overhead in OTFS is less than OFDM. Therefore, spectral efficiency of OTFS is higher than OFDM. OTFS also manages both fading and interference better than OFDM. In essence, OTFS overcomes the key limitations of OFDM by better managing the interference and fading, and by using Multiple-Input Multiple-Output (MIMO).
Spectral Multiplier Software Developed by Cohere Technologies has Tremendous Promise
A quick and non-comprehensive study on patent landscape for Delay Doppler (using Google Patent search), the technology behind OTFS, indicates that the top ten companies driving OTFS commercialization, sorted on Cooperative Patent Classifications (CPCs) percentage, in descending manner, are:
- Cohere Technologies (2.8%)
- LG Electronics (2.2%)
- Raytheon (1.7%)
- Motorola Inc. (1.7%)
- Acuson Corporation (1.5%)
- Qualcomm Inc. (1.3%)
- Kabushiki Kaisha Toshiba (1.2%)
- Huawei Technologies Co., Ltd (1.2%)
- Samsung Electronics Co., Ltd (1.1%)
- Uhnder, Inc. (1.1%)
Cohere has been a pioneer in OTFS technologies and holds more than one hundred patents related to OTFS. Leading TEMs, such as Nokia and Ericsson, are also active in this space, through partnership with Cohere as well as hiring OTFS specialists for their own in-house research. One of Mobile Network Operators (MNO) market needs, higher spectral efficiency, has already been productized with Cohere Technologies' Universal Spectrum Multiplier (USM) software that offers better orthogonal beam management, translating to better Multi-User MIMO performance. However, reducing PA power consumption has not been addressed yet, which could be the next frontier in radio network development.
Leadership of Major TEMs in OTFS Commercialization Will Secure OTFS's Place in 6G Standard
The industry has not yet reached consensus, or even agreement, that OTFS will be a candidate technology for 6G. Solving the two main challenges discussed above is the first stem, but there are also many barriers of entry for the new technology to become part of the standard. These include:
- The majority patent holder, and expert, for OTFS is Cohere, not the usual dominant companies in 3GPP. This means that incumbent technology providers may steer the discussion away from OTFS and towards their own expertise.
- OTFS is backwards compatible to OFDM, but will likely introduce a completely new user interface, meaning that MNOs will need to invest in completely new Radio Access Network (RAN) infrastructure when 6G is commercialized.
- Technical limitations still remain with a full implementation of OTFS, but processing capabilities will likely evolve over the next few years.
Nevertheless, despite its challenges, OTFS is a promising technology that will likely play a part in future standards. According to ABI Research insights, major TEMs are now investing in OTFS R&D, meaning that they also see a future in this new technology.