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.

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.

Narrowband Internet of Things (NB-IoT) is one of the most promising low-power wide-area technologies to support low cost, massive connection, deep coverage, and low-power consumption. This article proposes a complexity-effective narrowband secondary synchronization signal (NSSS) detection scheme for the cellular NB-IoT communication system. By taking advantage of the NSSS sequence, the search space of NSSS hypotheses is reduced by decoupling the detection of complementary Walsh sequence and Zadoff-Chu sequence in a sequential manner. Such a detection strategy allows reduced-complexity NSSS detection in the NB-IoT system. Both numerical and simulation results are presented to verify the effectiveness of the proposed NSSS detection scheme. The simulation results show that the proposed NSSS detector achieves a considerable complexity reduction at the cost of some performance degradation, compared to the conventional NSSS detector.

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.

This letter proposes a low complexity integer frequency offset (IFO) estimation scheme in an orthogonal frequency division multiplexing (OFDM) based digital radio mondiale plus (DRM+) system with nonuniform phased pilot symbols. To reduce the computational complexity, the pilot symbols used for frequency estimation in the DRM+ system are partitioned into a number of pilot subsets, and pilots in each subset are phase-rotated to have a unique phase so that the estimator is made computationally efficient.

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.

In this letter, a fine carrier frequency offset (CFO) estimator is proposed for ultra-wideband multiband orthogonal frequency division multiplexing (UWB MB-OFDM) systems. The proposed scheme uses a frequency-domain spreaded data symbol which is provided in the MB-OFDM system, thus removing the need of training symbols. Analytical expression of the mean square error (MSE) of the fine frequency synchronization scheme is reported, and simulation results are used to verify the theoretical analysis developed in this letter.

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.

In this letter, a constant-amplitude biorthogonal multicode (CABM) modulation is proposed. The proposed modulation is a biorthogonal modulation scheme that employs a constant-amplitude transmission of multicode signals by introducing a simple constant-amplitude coding scheme with redundant bits. The proposed CABM modulation can provide bandwidth efficiency up to the level (i.e., 9/16) of constant-amplitude orthogonal multicode (CAOM) modulation. We prove that our encoding scheme proposed in this letter provides this constant amplitude property. The bit-error rate (BER) performance expressions and the union bounds of the proposed CABM modulation and demodulation pairs are derived analytically. The results of the computer simulation and theoretical analysis performed show that the BER performance and the hardware complexity of the proposed CABM modulation are significantly better than those of a CAOM modulation

In this paper, a multi-coded variable spreading gain (MC-VSG) CDMA system employing a binary transmission of MC signals by introducing a level clipper, termed MC-VSG BNet system, is proposed for a possible candidate of wireless personal area network (WPAN) and 3G cellular applications. With an emphasis on the MC-VSG BNet physical layer and the system performance, we address the concise specification of the MC-VSG BNet system. From the receiver performance based on simulation results, in addition to simple receiver structure, an acceptable performance degradation of the MC-VSG BNet system over the existing DS/CDMA system is observed, while guaranteeing an high bit rate transmission.

A multi-coded CDMA system employing a variable spreading gain (VSG) approach is proposed for high-rate applications, which is based on two algorithms for selecting the multi-code set. From the simulation results, in addition to a simple receiver structure thanks to level clipping, the multi-coded VSG CDMA system provides a high bit rate transmission, while maintaining an acceptable performance degradation of the multi-coded VSG CDMA system over the existing DS-CDMA system.

This paper considers a channel estimation technique in a wireless personal area network (WPAN) system with complementary code keying (CCK) signaling over multipath fading channels. The performance of the proposed coherent detector is compared with that of a noncoherent detector, and a significant improvement of performance is observed in terms of the bit error probability.

We present a coarse frequency-offset synchronization technique for an OFDM-based transmission system with an emphasis on the Eureka-147 DAB receiver. The proposed frequency-offset synchronization algorithm using two defined correlation functions is shown to have high robustness against a large range of symbol timing offset with a moderate implementational complexity.

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.

The bit error rate (BER) expression for a proposed pipelined successive interference cancellation (PSIC) scheme in a direct sequence/code division multiple access (DS/CDMA) system is derived analytically. The proposed PSIC scheme is a pipelined modification of a successive interference cancellation (SIC) scheme. The numerical results show that the proposed PSIC scheme outperforms the SIC scheme from the viewpoints of the BER and the decoding delay performances.

The bit error probability expression for a RAKE receiver which employs a cochannel interference cancellation (IC) scheme with infinite number of cancellation stages is derived (which is referred to as the APL). According to the derivation in this paper, as the number of cancellation stages increases, the performance of a RAKE receiver with a multistage IC (MIC) scheme is observed to approach the APL only when the number of active users does not exceed the maximum user capacity, however it fails to approach that of a system with only a single user.

Multilevel trellis coded 16QAM with partially overlapped signal sets is introduced. It is shown with this scheme that one can achieve an asymptotic coding gain of 4.26 dB over QPSK with a bandwidth efficiency of 2.5 bit/sec/Hz. This result is due to the fact that multilevel trellis coding technique is more appropriate for utilizing the increased Euclidean distance of partially overlapped signal sets than its counterpart, TCM scheme. We explain this coding scheme in terms of performance, complexity, and set partitioning of partially overlapped 16QAM signals, and compare it with trellis coded 8PSK, 16QAM.

This paper presents threshold detection techniques for direct sequence code acquisition employing psuedo-noise (PN) matched filters. The probabilities of detection and false alarm are derived as a measure of the system performance in both nonfading and nonselective Rician fading channels. For received PN codes with different SNR, the proposed acquisition schemes (serial and parallel) are able to detect a desired threshold in the search mode so that this value is utilized as a threshold for the verification mode. It is shown that the serial scheme achieves lower probability of false alarm than the acquisition scheme based on the Neyman-Nearson criterion, giving comparable performance in terms of the probability of detection. On the other hand, it its shown that the parallel scheme is able to provide a sub-optimal threshold value for a wide range of SNR such that the mean acquisition time is minimized.