With the growing demand of serviceability for mobile terminals, mobile terminals are facing the problem of coexistence of multiple standards, functions and systems [1]. If traditional terminals are upgraded in the pattern of hardware upgrade to implement upgrading and capability enhancement, a large amount of electronic waste will be generated [2]. Therefore, it is necessary to break through the high-performance, open and reconfigurable software-defined radio (SDR) method of communication and perception. Faced the above problems, this paper proposes a generalized computational complexity analysis model, which gives a modular computational complexity analysis method by decoupling and separating the functions of the communication system.

This paper presents a novel integrated sensing and communication (ISAC) system based on multiple input multiple output (MIMO) and orthogonal frequency division multiplexing (OFDM) technologies with a non-orthogonal signal design that refines spectrum efficiency. Inspired by non-orthogonal multiple access (NOMA) scheme, we superimpose pseudo-random noise (PN) sequences and OFDM symbols in the power domain to enable simultaneous decimeter-level ranging and broadband communication over shared spectrum. A genetic algorithm optimizes power allocation to jointly achieve high-precision ranging and data throughput in the proposed frame. MIMO-based spatial processing can support high performance joint ranging and data detection. Experimental results demonstrate that the ranging precision of better than 1% of the actual distance and the data rate of over 1 Mbps can be achieved at a 6km distance under the signal-to-noise ratio (SNR) below -8dB, which confirm the system’s dual functionality and compatibility with legacy OFDM, offering a new direction for future integrated networks.

Unmanned Aerial Vehicles (UAVs) are critical in modern emergency response due to their high mobility. However, limited computing resources and energy supplies necessitate the use of UAV networks for collaborative inference. UAV intelligent tasks are often Deep Neural Networks (DNN)-based, with DNN partitioning enabling collaborative inference. However, executing DNN partitioning in a highly dynamic UAV network faces two challenges that have not been addressed in existing research: the time gap between the state sampling and the execution of the corresponding action based on that state, and the unknown trajectories in advance. The time gap requires predictive action decision-making. To address this, we model DNN partitioning and edge offloading with hybrid action decisions in dynamic, energy-harvesting UAV networks as a Predictive Markov Decision Process (P-MDP). The rapidly changing and previously unknown network topology significantly impacts channel and data transmission energy consumption, affecting DNN partitioning decisions. To better solve the action prediction problem, we use the Transformer module to extract motion features from recent time slots in the proposed Transformer-enhanced Multi-Agent Hybrid Action Proximal Policy Optimization (TE-MHAPPO) framework. Simulation results show that TE-MHAPPO reduces the reward which comprehensively considers task delay and energy consumption, by at least 12.1% compared to the state-of-theart MHAPPO. Additionally, its reward performance degradation with the increase in prediction time is at most 55.2% of that observed in the baseline.

For ultraviolet (UV) communication systems with discrete Poisson channel and photon-counting-based receivers, commonly used synchronization scheme is to perform correlation at the start of each frame, but this scheme is difficult to correct the error caused by clock frequency offset within the frame. In this paper, a UV communication system with our self bit synchronization scheme is proposed. It adopts on-off keying (OOK) modulation, and uses the real-time result of photon counting module to synchronize the counting window without any extra input. The proposed scheme regards the input signal envelope as rectangular waves, matches and merges obvious edges detected, and computes moving distance. Our system achieves a bit error rate (BER) of $1.5\times 10^{-4}$ at 25.6 kbps bit rate when the average photon amount in a single bit 1 duration is at about 40.

A power amplifier(PA) is inherently nonlinear device and is used in a communication system widely. Due to the nonlinearity of PA, the communication system is hard to work well. Digital predistortion (DPD) is the way to solve this problem. Using Volterra function to fit the PA is what most DPD solutions do. However, when it comes to wideband signal, there is a deduction on the performance of the Volterra function. In this paper, we replace the Volterra function with B-spline function which performs better on fitting PA at wideband signal. And the other benefit is that the orthogonality of coding matrix$A$could be improved, enhancing the stability of computation. Additionally, we use compressive sampling to reduce the complexity of the function model.

In this paper we consider a passive radar system which doesn't rely on the reception of reference signals from direct paths. A blind channel estimation based method is derived by exploring the relationship among the transmitted signal, the channel response and the received signal. With the help of this novel method, multiple incoming targets illuminated by a non-cooperative transmitter can be detected by a distributed radar system with at least two receivers. Numerical results demonstrate the feasibility and accuracy of the proposed method and some characteristics of the detector, namely, the performance as a function of the signal to noise ratio (SNR) and the number of radar receivers.

Terrestrial broadcasting signals have been recognized as promising candidates for positioning and navigation needs. However, in some terrestrial broadcasting networks, which are usually single frequency networks, the transmitter confusion problem poses a huge obstacle to almost all positioning algorithms. Without knowing the transmitter identities, measurements can't be associated to transmitters coordinates properly, thus leaving receiver coordinates unable to be estimated. Meanwhile, as the exact transmission delay is usually hard to estimate, the time difference of arrival (TDoA) based positioning is widely used. In this paper, a novel TDoA based localization method is proposed to realize positioning in single frequency networks. With the proposed method, the receiver can estimate its own position when transmitter identities are missing from the signals. Simulation results verify the feasibility and accuracy of the method and discussions regarding its properties are given.

Broadcasting signals are considered as promising candidates for positioning and navigation needs thanks to its many advantages. However, most broadcasting networks are single frequency networks (SFN), in which the transmitter confusion problem poses a huge obstacle. Since all transmitters in a SFN broadcast the same signal simultaneously, the receiver cannot obtain the transmitter identities, thus can no longer determine its position. In this paper, a novel angle of arrival (AoA) based position method is proposed to realize positioning in SFN. The proposed method can overcome the transmitter confusion problem without modifications on the broadcasting sequences. Simulation results confirm that the proposed method can realize positioning in SFN with high accuracy.

The visible light communication (VLC) and wireless LAN (WLAN) heterogeneous network is considered as a highly competitive candidate for the next generation indoor wireless communication. VLC can provide high data rate as downlink mechanism while WLAN supports reliable connectivity and covers uplink needs. In such heterogeneous systems, vertical handover (VHO) is critical for the system reliability and performance. This paper proposes an improved design of the dwell timer used in VHO process by introducing a dynamic dwell timer based on prediction. Simulation results show that the proposed design outperforms benchmark designs by avoiding unwise handovers while achieving a longer connection time and higher average data rate. Simulations also prove that the proposed design is applicable to different environments and user behaviors.

Combined with client pairing on nonorthogonal multiple access (CP-NOMA), carrier sense multiple access/collision avoidance (CSMA/CA) can provide more connectivity for clients in downlink phase and alleviate the low transmission efficiency from rate anomaly problem. Compared with conventional CSMA/CA system, the proposed enhanced CSMA/CA with CP-NOMA can save about half of the time cost to send signaling overhead and provide improvement in the efficiency of data transmission. Similar to saturated throughput, the long-term average rate is defined and used to illustrate the performance of the proposed method. Considering the criterion of the fairness and the received signal to noise ratio (SNR), the selection of client pairing in NOMA could be optimized to maximize the data transmission rate in NOMA. Providing the channel access for more clients, the efficiency of the downlink transmission is enhanced in the proposed scheme. In the application of Internet of Things (IoT), The enabling technology supporting more clients in connectivity really makes a big difference. Besides, the enhanced CSMA/CA with CP-NOMA is compatible with conventional CSMA/CA system.

Spatial modulation (SM) is a modulation scheme that exploits the spatial dimension of multiple-input multiple-output (MIMO) channels to encode the transmitted information. It is shown in this paper that, by properly rotating the phase of the transmitted symbols, the minimum Euclidean distance (MED) of the constellation of the received symbols can be enlarged and hence the error performance can be improved. Moreover, we propose an algorithm that incorporates an iteration process to design the phase-only pre-scaling factors, which only rotate the phases of different transmitted symbols according to the instantaneous channel realization. Simulation results demonstrate that the proposed method is capable of outperforming the conventional SM scheme and other pre-scaling SM schemes.

The orthogonal frequency division multiplexing (OFDM) system is widely adopted in high-speed wireless communication systems. Different from the single carrier transmission scheme, OFDM system is extremely sensitive to the carrier frequency offset (CFO). Several frequency estimation methods have been proposed to extract and compensate the CFO. However, conventional estimation methods get some trouble in correctly extracting the integer CFO in strong echo channels. In this paper, a novel frequency estimation method, using PN sequence embedded in frequency domain OFDM data, is introduced for time-domain synchronous OFDM. The method uses correlation result between PN sequence and OFDM data to extract the integer CFO. Simulation result proves that the new method precisely extract the integer CFO in various channels almost without interference on data.

An error transfer chart is introduced to trace the iterative process of the decision feedback equalizer for the single-carrier modulation. In the investigated iterative MF-DFE structure, the forward filter is set to the matched filter to maximize the signal power, while the feedback filter is used to cancel the inter-symbol interference. MMSE detection is applied to minimize the decision error power. The trajectory of iterations is shown in the error transfer chart, in which MF-DFE maps a decision error power to an SINR and MMSE detection further converts the SINR to a new decision error power. The final state of iterations is shown to be the intersection of the MMSE curve and error power transfer curve corresponding to the MF-DFE algorithm. It is shown by simulation that the error transfer chart is a useful tool to analyze the convergence of non-linear iterative equalizers.

This paper develops a low-complexity channel estimation (CE) scheme based on compressive sensing (CS) for time-domain synchronous (TDS) orthogonal frequency-division multiplexing (OFDM) to overcome the performance loss under doubly selective fading channels. Specifically, an overlap-add method of the time-domain training sequence is first proposed to obtain the coarse estimates of the channel length, path delays, and path gains of the wireless channel, by exploiting the channel's temporal correlation to improve the robustness of the coarse CE under the severe fading channel with long delay spread. We then propose the priori-information aided (PA) iterative hard threshold (IHT) algorithm, which utilizes the priori information of the acquired coarse estimate for the wireless channel and therefore is capable of obtaining an accurate channel estimate of the doubly selective fading channel. Compared with the classical IHT algorithm whose convergence requires the l2norm of the measurement matrix being less than 1, the proposed PA-IHT algorithm exploits the priori information acquired to remove such a limitation and to reduce the number of required iterations. Compared with the existing CS-based CE method for TDS-OFDM, the proposed PA-IHT algorithm significantly reduces the computational complexity of CE and enhances the CE accuracy. Simulation results demonstrate that, without sacrificing spectral efficiency and changing the current TDS-OFDM signal structure, the proposed scheme performs better than the existing CE schemes for TDS-OFDM in various scenarios, particularly under severely doubly selective fading channels.

Conventional time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) systems have the difficulty to support 256QAM or higher-order modulations and suffer from performance loss, especially under the severe fading channels with long delays. In this letter, a simultaneous time-frequency channel estimation method based on compressive sensing (CS) is proposed to solve this problem. First, the auxiliary channel information is obtained by exploiting the signal structure of TDS-OFDM. Then, a very few frequency-domain pilots in the OFDM block are used to acquire the accurate channel impulse response under the framework of CS. Besides, the auxiliary channel information is utilized to further reduce the complexity of the classical CS algorithm. Simulation results show that the proposed scheme can well support 256QAM under fading channels with long delays and have better performance than the conventional schemes.

A novel compressive sensing (CS) based narrowband interference (NBI) cancellation approach for power line communication (PLC) systems is proposed in this paper. The repeated training sequences of the preamble in PLC systems are utilized for differential measuring to acquire the measuring vector. Under the CS framework, the sparse high-dimensional NBI signal can be reconstructed from the measuring vector of much smaller size obtained through the proposed CS-based differential measuring (CSDM) method. It is verified by theoretical analysis and simulations that the proposed method outperforms conventional anti-NBI methods under the PLC channel.

In [1], an orthogonal frequency division multiplexing (OFDM) preamble based on distance detection (PBDD) is proposed for broadcasting systems. However, traditional correlation based signaling demodulation will completely fail to work under severe transmission conditions with ultra-long delay spread 0dB echo. In this paper, a new transmission parameter signaling (TPS) detection method is proposed for PBDD structure. Compared with the conventional signaling detection method, our method works much better when the maximum channel delay spread is close to guard interval (GI) length. Simulation results demonstrate that the proposed approach offers significant performance improvement in most cases with more accurate signaling detection performance.

In this paper, we propose a time-domain oversampled receiver for orthogonal frequency division multiplexing (OFDM) in underwater acoustic communication. Without changing the structure of the transmitter, significant gains are acquired by time- domain oversampling at the receiver. Using time- domain oversampling, the energy of transmitted symbols is concentrated on the first N subcarriers, while additive Gaussian noises are distributed in all the subcarriers. Because of the sparsity of underwater acoustic channels, most energy of the channel impulse responds is concentrated on a few paths, and other positions are submerged by noises. Channel estimation based on the discrete Fourier transform is employed to eliminate noises. After estimating the energy of additive Gaussian noises, the truncation of channel impulse responds eliminates the majority of noises. Simulations are implemented in multipath channels and fading channels. Without changing the structure of the transmitter, the proposed oversampled receiver outperforms the conventional receiver in bit error rate (BER) performances significantly, with a little increased computational complexity.

In time-domain synchronous OFDM (TDS-OFDM) system for digital television terrestrial multimedia broadcasting (DTMB) standard, the baseband OFDM signal is upsampled and shaping filtered by square root raised cosine (SRRC) filter before digital-to-analog converter (DAC). Much of the work in the area of timing synchronization for TDS-OFDM focuses on frame synchronization and sampling clock frequency offset recovery, which does not consider the sampling clock phase offset due to the upsampling and SRRC filter. This paper evaluates the bit-error-rate (BER) effect of sampling clock phase offset in TDS-OFDM system. First, we provide the BER for M-order quadrature amplitude modulation (M-QAM) in uncoded TDS-OFDM system. Second, under the condition of the optimal BER criterion and additive white Gaussian noise (AWGN) channel, we propose a near optimal sampling phase estimation criterion based on frequency-domain response. Simulations demonstrate that the proposed criterion also has good performance in actual TDS-OFDM system with channel coding over multipath channels, and it is superior to the conventional symbol timing recovery methods for TDS-OFDM system.

In this paper, we propose an improved preamble structure based on distance detection using a pair of training sequences in frequency domain, whereby self-adaptive algorithm is introduced. Guard interval with cyclic prefix (CP) property is used to achieve better signalling transmission performance under frequency selective fading channel. Moreover, delay and differential operation is applied to eliminate continuous wave (CW) interference. Theoretical analyses and simulation results show that the proposed scheme has superior signalling demodulation and synchronization performances to the existing methods.

Orthogonal frequency division multiplexing (OFDM) is a promising technology for the next-generation optical transmission systems beyond 100 Gb/s. To further improve the spectral efficiency and system reliability, we propose a flexible coherent zero padding OFDM (CO-ZP-OFDM) scheme with signaling-embedded preamble and polarization-time-frequency (PTF) coded pilots for high-speed optical transport networks. Our judicious design embeds signaling in the specially designed preamble whose Delta-like correlation function helps to simultaneously achieve very accurate timing and frequency synchronization. Unlike the periodically inserted training symbols, the PTF-coded pilots are properly distributed within the time-frequency grid of the ZP-OFDM payload symbols and used to realize low-complexity multiple-input multiple-output (MIMO) channel estimation at high accuracy. Compared with the conventional optical OFDM systems, CO-ZP-OFDM increases payload by about 6.68%, and the low-density parity-check (LDPC) coded bit error rate only suffers from no more than 0.3 dB compared with the back-to-back case even when the channel dispersion impairments are severe.

Frequency domain equalization (FDE), as a linear equalizing method, is widely adopted in many applications with either OFDM or single carrier (SC) modulation. This paper analyzes the the noise transfer effect, a case for noise colorization, after FDE. This process is investigated for CP-OFDM, ZP-OFDM and SC systems where SC is treated as a multi-carrier modulation with the number of subcarriers equal to 1. Based on this analysis and by assuming the de-mapping independence among subcarriers, the average channel capacity for the systems is derived. We have proved that the capacity of the CP-OFDM system is at least equal to that of ZP-OFDM in both low and high SNR scenarios and that the capacity of the SC system is no greater than that of either ZP-OFDM or CP-OFDM systems. In a multi-path channel, if the IDFT size of the OFDM symbol is not equal to the DFT size of the equalizer, the leakage of the enhanced noise in a deeply faded sub-channel will cause the loss of capacity in adjacent sub-channels and the overall average capacity is thus reduced.

This paper presents a decision directed frequency and clock tracking scheme to improve the spectrum efficiency of burst mode OFDM transmission with frequency selective channel. OFDM divides one broadband channel to parallel narrowband subchannels of different channel characteristics. In this scheme, the subcarriers with better attenuation are selected out to do the decision-directed based clock and frequency tracking. a novel phase error detection method is proposed which keeps the hard decision working well when tracking is performed. Furthermore, Particular algorithm is designed to ensure the carrier frequency offset and sampling frequency offset could be solved out from detected phase error. Simulations illustrate that the new scheme can work well in typical system.

To improve the system capacity of conventional orthogonal frequency division multiplexing (OFDM) systems, the layered modulation OFDM scheme is proposed. The modulated OFDM symbols are separated into two layers as differential modulated symbols and coherent symbols. The differential symbols are used as pilots, which are combined with the coherent modulated data and sent out by the transmitter. At the receiver side, the data in pilot position will be recovered after the differential demodulation. The recovered differential symbols will be used for channel estimation to demodulate the coherent symbols. Furthermore, the differential modulated data can employ low reception threshold and low complexity demodulator, which will facilitate the usage in mobile TV transmission. Simulations show the two layers' reception can be compatible with each other.

In broadband wireless communication systems, single-carrier transmission with frequency domain equalization (SC-FDE) is regarded as an alternative modulation technique to the orthogonal frequency division multiplexing (OFDM). Compared with OFDM systems, SC-FDE has similar implementation complexity and performance. However, SC-FDE with linear equalizer will suffer from serious performance deterioration under deep frequency selective fading channels. An effective method to solve this problem is to introduce non-linear decision feedback equalization (DFE) to SC-FDE. In this paper, a low complexity iterative decision feedback equalizer in the frequency domain for single- carrier systems is proposed. Based on the minimum mean square error (MMSE) criterion, a simplified parameter estimation method is introduced to calculate the coefficients of the feed-forward and feedback filters, which reduces the implementation complexity of the equalizer. Simulations show that the performance of the proposed algorithm is similar to the traditional iterative block DFE (IBDFE) under various multipath fading channels but with lower complexity.