Automatic modulation recognition (AMR) is a key enabler for intelligent spectrum utilization in 5G-and-beyond wireless systems, requiring both high classification accuracy and low computational complexity. This paper proposes a lightweight hybrid deep learning framework, termed CBLGNet, that integrates convolutional neural networks (CNN), bidirectional long short-term memory (BiLSTM), and gated recurrent units (GRU) for efficient AMR from raw in-phase and quadrature (I/Q) samples. The CNN extracts compact spatial representations, while the BiLSTM–GRU structure captures bidirectional temporal dependencies with reduced parameter complexity. Unlike existing hybrid models that rely on deep recurrent stacks or heavy dense layers, the proposed architecture achieves effective feature fusion with a compact parameter budget. Evaluations on the RML2016.10a and RML2016.10b datasets demonstrate that CBLGNet achieves 93.39% classification accuracy, outperforming several state-of-the-art AMR methods while maintaining low computational cost.

Beamforming optimization in 6G networks is essential for ensuring energy-efficient and interference-aware transmission, where ultra-reliable low-latency communication (URLLC) and scalable antenna technologies play a key role. Classical optimization methods face scalability challenges, making real-time beamforming infeasible. This paper applies the quantum approximate optimization algorithm (QAOA) to minimize transmit power while ensuring signal quality constraints. The problem is formulated as a quadratic unconstrained binary optimization (QUBO) and solved using quantum simulation. Simulation results demonstrate that QAOA achieves lower transmit power compared to classical solvers, with faster convergence and improved efficiency. These findings suggest that quantum computing can significantly enhance beamforming optimization, paving the way for its integration into future wireless networks.

This article proposes an effective joint sidelink secondary synchronization signal (S-SSS) and carrier frequency offset (CFO) detection method for device-to-device-based new radio vehicle-to-everything networks. In order to improve the S-SSS and CFO detection performance, the proposed method uses a group-by-group correlation between four consecutive sidelink synchronization signals. The benefits and drawbacks of the proposed detection scheme are presented, and a theoretical analysis is derived, which is further discussed by means of simulation results. Both analytical results and simulations show that the proposed solution attains an improved detection performance using a group-wise correlation with slightly increased complexity, compared to existing detection algorithms.

This article proposes a reduced complexity synchronization signal detection scheme in a narrowband Internet of Things (NB-IoT) system. By detecting the narrowband secondary synchronization signal (NSSS), both physical cell ID (PCID) and radio frame number (RFN) are jointly obtained during the initial cell search procedure in NB-IoT. To facilitate reduced complexity joint detection of the PCID and RFN, we propose an NSSS subcarrier grouping method by balancing the phase offset among NSSS subcarriers. The advantages and drawbacks of the proposed joint detector are presented by comparing the conventional joint detector in terms of performance and complexity. The probability of detection failure of the proposed detector is theoretically derived, which is further validated by means of simulation results. Both analytical results and simulations show that the proposed solution significantly decreases the computational burden with negligible performance loss, compared to the conventional detectors.

Synchronization is a challenging problem of device-to-device (D2D) communications, particularly when D2D devices are out-of-network coverage. This article proposes an efficient initial synchronization method for D2D communication in a long term evolution system. The proposed synchronization approach is based on the correlation between both received primary sidelink synchronization signal and secondary sidelink synchronization signal to remove the effects of channel fading and symbol timing offset (STO). This design facilitates reduced-complexity joint detection of carrier frequency offset, sidelink synchronization signal, and cyclic prefix (CP) mode during the initial synchronization procedure. Simulation results show that the proposed synchronization scheme achieves robust and low-complexity detection of carrier frequency offset, sidelink synchronization signal, and CP mode when there is a nonnegligible STO or frequency-selective fading distortion.

In this article, a complexity effective and robust cell search method is proposed for machine-type communication in a long-term evolution system. The correlation between the primary synchronization signal (PSS) and secondary synchronization signal (SSS) in the frequency domain is exploited to remove the effect of channel fading distortion and symbol timing offset. This design facilitates robust synchronization of the carrier frequency offset, sector ID, and duplex mode without performing hypothesis testing on SSS candidates, followed by the detection of group ID. Both theoretical and experimental results are presented to justify the effectiveness of the proposed cell search scheme. The simulation results show that the proposed method achieves robust and reduced-complexity cell search when there are nonnegligible residual symbol timing error and frequency-selective fading distortion, compared to existing methods.

The main features for future machine-type communication (MTC) cellular networks are to support low-power consumption, low-bandwidth, and long-range communication. One of the most challenging issues to meet these goals in the MTC cellular network is a low-complexity and reliable initial synchronization. To address this issue, in this article an efficient joint detection of integer carrier frequency offset (IFO) and cell identity (CID) is proposed for MTC in a long-term evolution (LTE) system. Unlike the conventional approach, the primary synchronization signal (PSS) and secondary synchronization signal (SSS) transmitted in the LTE-MTC system are used together to remove the effect of channel fading and symbol timing offset (STO). This design facilitates robust detection of the IFO and CID in the presence of residual STO without priori information on the SSS. The grouping of PSS subcarriers is integrated for joint detection, which plays an important role on reducing computational load. Both analytical and simulation results are provided to corroborate the feasibility of the proposed method. It has been demonstrated that the unique characteristics of the PSS and SSS sequences are effectively used for robust cell search in the presence of residual STO, compared to existing methods.

A key challenge associated with cellular-based machine-type communication (MTC) is to provide better coverage enhancement (CE) along with low power consumption for MTC user equipments (UEs). Due to the limitation on total power allowed for transmission, it is required to estimate frequency error in very low signal-to-noise ratio condition. In this article, an effective frequency offset estimation method is presented for MTC in a long term evolution system. The proposed method applies the repetitive nature of the MTC physical broadcast channel to the weighted least-squares estimation technique. Both analytical and simulation results are provided to corroborate the feasibility of the proposed method. It is shown that the proposed estimation scheme is more efficient for CE of MTC UEs, compared to the existing method.

In this letter, we address the beamforming in full-duplex self-energy recycling relay system, where an amplify-and-forward relay delivers the source message to the destination in a single time slot while recycling a portion of its RF energy through energy harvesting. The signal received at the realy is divided into two circuits, one for the full-duplex relaying and the other for the energy harvesting. The beamforming vectors and the power division ratio at the relay are optimized to maximize the harvested energy while maintaining a certain reception quality threshold at the destination. Simulation results show various advantages and trade-offs of the proposed system.

A cooperative communication has been frequently studied because it provides reliability to the previous communication system without the addition of antenna. However, in a cooperative communication, the throughput of the communication system is decreased by half because each station cannot transmit own signal for relaying process. To overcome above limitation and provide more reliability, we propose and analyze the mutual decode-and-forward (DF) cooperative communication for orthogonal frequency-division multiple access (OFDMA) based mobile WiMAX system with single antenna in the Rayleigh fading channel environment. By adopting the proposed scheme, the performance of the mobile WiMAX system is improved in proportion as the quality of inter-user channel is increased.

An efficient MIMO signal detection technique with low complexity is presented for MIMO-OFDM systems. The proposed technique has a feature of combined QRD-M and DFE detection. In our detection technique with M transmit antennas, after QRD-M detection is executed for first T detection steps, DFE detection is executed for last M - T detection steps. This approach is simple and has low complexity, because the computations for QRD-M is limited by the newly adopted parameter T. From simulation results, the complexity of the proposed technique with 4 times 4 and T = 2 is reduced by 61% compared with that of the conventional QRD-M at the expense of about 0.7dB degradation of BER performance at BER=10-4. The simulations are executed in Ricean and Rayleigh channel models. And the simulation of proposed technique is executed by using estimated channel. Through the simulations, it is ascertained that the proposed detection can be used for Ricean and Rayleigh channel models as well as estimated channel.

A combination of OFDM with FDMA called OFDMA is regarded as a promising solution for improving the performance of BWA with multiple users. Although transmit diversity is clearly advantageous on OFDMA systems, it may not be possible that practical OFDMA systems have more than two antennas due to size, cost, or hardware limitations. Cooperative networks aim to utilize the available terminals as a collection of distributed antennas for the transmission of signals from one end of the network to the other. This paper focuses on design and performance evaluation of IEEE 802.16 MIMO-OFDMA systems with cooperative diversity. In this paper, for high-rate and reliable transmission, efficient transmission code is proposed.

This paper describes an adaptive timing synchronization scheme and DC-offset compensation technique for a short-ranged Bluetooth system. The synchronization scheme estimates the variance of the partial-band interference, which is utilized for the trigger threshold value of the inquiry scan and page scan states, while DC-offset compensation scheme is designed using the access codes which are known to each Bluetooth device. Numerical results show the proposed synchronization algorithm is robust to the partial-band noise interference and of low complexity. Also, the new DC-offset compensation method shows more reliable estimation ability of DC-offset than the existing method without extra hardware burdens.