Search

Orbital angular momentum (OAM) mode multiplexing has the potential to achieve high spectrum-efficiency communications at the same time and frequency by using orthogonal mode resource. However, the vortex wave hollow divergence characteristic results in the requirement of the large-scale receive antenna, which makes users hardly receive the OAM signal by size-limited equipment. To promote the OAM application in the next 6G communications, this article proposes the cooperative OAM wireless (COW) communication scheme, which can select the cooperative users (CUs) to form the aligned antennas by size-limited user equipment. First, we derive the feasible radial radius and selective waist radius to choose the CUs in the same circle with the origin at the base station. Then, based on the locations of CUs, the waist radius is adjusted to form the receive antennas and ensure the maximum intensity for the CUs. Finally, the cooperative formation probability is derived in the closed-form solution, which can depict the feasibility of the proposed COW communication scheme. Furthermore, OAM beam steering is used to expand the feasible CU region, thus achieving higher cooperative formation probability. Simulation results demonstrate that the derived cooperative formation probability in mathematical analysis is very close to the statistical probability of cooperative formation, and the proposed COW communication scheme can obtain higher spectrum efficiency than the traditional scheme due to the effective reception of the OAM signal.

Orbital angular momentum (OAM) and rate splitting (RS) are the potential key techniques for the future wireless communications. As a new orthogonal resource, OAM can achieve the multifold increase of spectrum efficiency to relieve the scarcity of the spectrum resource, but how to enhance the privacy performance imposes crucial challenge for OAM communications. RS technique divides the information into private and common parts, which can guarantee the privacies for all users. In this paper, we integrate the RS technique into downlink OAM-MIMO communications, and study the precoding optimization to maximize the sum capacity. First, the concentric uniform circular arrays (UCAs) are utilized to construct the downlink transmission framework of OAM-MIMO communications with RS. Particularly, users in the same user pair utilize RS technique to obtain the information and different user pairs use different OAM modes. Then, we derive the OAM-MIMO channel model, and formulate the sum capacity maximization problem. Finally, based on the fractional programming, the optimal precoding matrix is obtained to maximize the sum capacity by using quadratic transformation. Extensive simulation results show that by using the proposed precoding optimization algorithm, OAM-MIMO communications with RS can achieve higher sum capacity than the traditional communication schemes.

The vortex wave mode provides wireless communications with a new orthogonal resource for the multifold increase of spectrum efficiency. The rate splitting multiple access (RSMA) technique realizes the flexible decoding at the user equipment (UE) by dividing the information into private and common parts. This letter proposes the RSMA based vortex wave (RBVW) communications, which can enhance the access capability and privacy performance of vortex wave communications. By using the uniform circular array, we design the transmission framework of RBVW communications, where different user groups use different vortex wave modes and users in the same user group utilize RSMA to obtain the information. The UE channel model and achievable rate are derived for RBVW communications. Simulation results demonstrate that compared with the traditional schemes, RBVW communications can obtain higher achievable rate, especially for long distance transmission.

SnO2 nanowires were synthesized by thermal evaporation, and the field emission characteristics of SnO2 nanowires are investigated in detail. The results show that the turn-on field is as low as 1.39?V/µm. And the fluctuation of field emission currents is as low as 2.8% for 24?h. The results reveal that SnO2 nanowires hold promise for field emission display application.