In this letter, we propose two novel, yet efficient, user pairing schemes for non-orthogonal multiple access (NOMA) in 3D visible light communication (VLC). Our analysis is carried out assuming different heights for the users’ location as well as two dynamic power allocation strategies. Performance gains are attained when compared the proposed schemes with NOMA without user pairing and with orthogonal multiple access (OMA). The effects of the key system parameters on the overall performance are investigated and insightful discussions are drawn.

The sixth generation (6G) wireless technology aims to achieve global connectivity with environmentally sustainable networks to improve the overall quality of life. The driving force behind these networks is the rapid evolution of the Internet of Things (IoT), which has led to a proliferation of wireless applications across various domains through the massive deployment of IoT devices. The major challenge is to support these devices with limited radio spectrum and energy-efficient communication. Symbiotic radio (SRad) technology is a promising solution that enables cooperative resource-sharing among radio systems through symbiotic relationships. By fostering mutualistic and competitive resource sharing, SRad technology enables the achievement of both common and individual objectives among the different systems. It is a cutting-edge approach that allows for the creation of new paradigms and efficient resource sharing and management. In this article, we present a detailed survey of SRad with the goal of offering valuable insights for future research and applications. To achieve this, we delve into the fundamental concepts of SRad technology, including radio symbiosis and its symbiotic relationships for coexistence and resource sharing among radio systems. We then review the state-of-the-art methodologies in-depth and introduce potential applications. Finally, we identify and discuss the open challenges and future research directions in this field.

The Internet of Things revolution has profoundly impacted wireless communication systems. Access to high data rates is now just as important as low power operation. The use of incident millimeter-wave (mmWave) signals for ambient backscatter communication (AmBC) has shown significant promise for delivering high data rates. However, due to channel sparsity, incident signal availability to backscatter devices (BDs) at mmWave is erratic. In order to address the incident signal inaccessibility problem and enable high data-rate AmBC, this paper presents an efficient beam selection method in the beamspace millimeter-wave symbiotic radio system. The proposed method improves the overall system’s sum-rate performance by up to 30% while ensuring signal accessibility to BDs.

Power efficiency is a critical metric for a sustainable 6G network. The emergence of integrated sensing and communication (ISAC) services leads to significant power consumption due to additional signal transmission for sensing. An ISAC beamforming is an efficient transmission method for reducing power consumption in mmWave multi-input multi-output (MIMO) systems while meeting the requirements of communication users (CUs) and sensing users (SUs). This approach is only feasible when both users are within the coverage of the same beam. Otherwise, separate beams are required which results in high power consumption. In this study, we propose a novel time-domain scheduling method for ISAC beamforming to achieve high-power efficiency. The performance gains compared to conventional scheduling method are demonstrated for the different number of users, periodicity values, and user distribution ratios.

This study proposes an orthogonal frequency division multiplexing (OFDM) based scheme to achieve interference-free backscatter communications (BC) in a symbiotic radio system. In this scheme, the backscatter device performs frequency shift keying (FSK) modulation to shift the primary signal, i.e., the OFDM symbols transmitted from a base station, in the frequency domain to transmit its information. Symbiotically, the base station empties specific subcarriers within the band so that the received frequency-shifted signals from the backscatter device and the primary signal are always orthogonal. Based on the empty subcarrier placement and the corresponding FSK modulation, we propose three schemes including on-off keying (OOK), FSK-1, and FSK-2. Specifically, the first scheme integrates FSK into OOK modulation while the second and the third schemes are based on the conventional FSK modulation with different in-band null-subcarrier allocation. To address the channel estimation challenge for the signals arriving from a backscatter device, we consider a non-coherent detector for obtaining the information from the backscatter signal at the receiver. We derive the bit-error rate performance of the detector theoretically. The comprehensive simulations show that the proposed approach achieves a lower bit-error rate up to $10^{-4}$ at 30 dB with BC by eliminating direct link interference.

This article presents a unique lightweight and interference-free backscatter communication (BC) scheme based on zero tail discrete Fourier transform spread OFDM (ZT DFT-s-OFDM) waveform signals. In the proposed approach, the ZT region of the waveform is exploited to accommodate backscatter transmissions using delay shift keying (DSK) modulation. A backscatter device (BD) equipped with modulator based on acoustic-wave delay circuits conveys information by introducing deterministic delay shifts within the uncorrupted ZT portion of the ZT DFT-s-OFDM symbol, thus ensuring complete time-domain separation between the primary and BD signals. This approach effectively eliminates direct-link interference (DLI) while maintaining full compatibility with conventional receivers. To address the channel-estimation challenge, a low-complexity, non-coherent detector is developed, and its analytical performance is derived and validated through simulation. The simulations show consistency between the analytical and simulation results, demonstrating that the proposed design achieves a probability of missed detection (P_MD) as low as 10⁻³ at 30 dB, therefore, confirming its robustness and suitability for low-power BC applications.