News on China's scientific and technological development.

Recently, Liu Lei, a researcher at the School of Information and Electronic Engineering of Zhejiang University, and Professor Zhang Chaoyang, in collaboration with Chi Yuhao and Li Ying at the School of Communication Engineering of Xidian University, have made breakthrough progress in new multi-carrier modulation technology. The relevant research results were published in the authoritative wireless communication journal " IEEE Wireless Communication Letters " () under the title " Interleave Frequency Division Multiplexing " .

Background : In recent years, with the increasing number of high-speed mobile communication applications ( such as high-speed rail, low-orbit satellites, etc. ) , the existing orthogonal frequency division multiplexing (OFDM) has been severely affected by inter-carrier interference, resulting in performance degradation. To solve this problem, in 2017 , Cohere , a US company, proposed the orthogonal time-frequency-space (OTFS) modulation technology; Huawei proposed the analog radio frequency division multiplexing (AFDM) modulation technology in 2021. The core principle of OTFS and AFDM is to construct a sparse equivalent channel matrix to achieve a balance between performance and complexity. It is foreseeable that in the future 6G technical standards, modulation technologies that can support static and high-speed mobile communications will occupy an important position. The 6G communication standard patent layout report released by the State Intellectual Property Office in 2023 pointed out that in OTFS technology, Cohere, a US company, has a large number of high-quality basic patents, accounting for 68.9% of the world's patent applications , and has formed a certain technical barrier. Although Chinese universities have certain R&D capabilities in the field of OTFS technology, the patent risk is relatively high because they cannot bypass the basic patents.

Challenges and goals : Currently, OTFS and AFDM have not fundamentally solved the public problem of non-stationarity of time-varying multipath channels, and are also facing the challenge of lack of efficient and low-complexity detection algorithms. Therefore, it is urgent to explore a new generation of multi-carrier modulation technology, study the statistical stabilization mechanism of channels, overcome the non-stationarity problem of time-varying multipath channels, and achieve high-speed, high-reliability information transmission close to the capacity limit of time-varying multipath channels.

IFDM modulation : To address this technical challenge and break through the blockade of OTFS technology patents, this work first proposed a new interleave frequency division multiplexing (IFDM) modulation technology ( Figure 1) . Through the simple structure of inverse Fourier transform and random interleaving, a random fully dense equivalent channel matrix ( Figure 2) was innovatively constructed to ensure that the signal undergoes a sufficient statistically stable channel fading process, thereby approaching the time-varying multipath channel capacity.​