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The unmanned aerial vehicle (UAV) assisted communication can significantly improve the coverage and spectrum efficiency of the Internet of Things (IoT). One main feature of IoT is short packet communication (SPC), in which the data transmission uses finite block-length codewords. The transmission rate and the packet error rate will affect the effective throughput of the IoT. In this paper, we investigate the impact of SPC on the performance of UAV-enabled spectrum sharing network. Specifically, the optimization of energy efficiency (EE) in the UAV communication system is considered since the battery of the UAV is usually limited. We design the packet error rate, the sensing duration, the normalized sensing threshold and the UAV’s transmit power to maximize the EE under the constraint that the primary user is sufficiently protected. Since the system parameters are intertwined with each other, we employ a successive optimization algorithm to solve the optimization problem by dividing it into three subproblems. Then, an efficient iterative algorithm is proposed to obtain the optimal parameters. Simulation results reveal that the proposed algorithm can converge to global optimal value and has better EE performance than other benchmark schemes. And there is a fundamental tradeoff between the throughput and the EE.

Orthogonal frequency division multiplexing offset-QAM (OFDM/OQAM) is a promising multicarrier transmission technique for its merits such as operating without cyclic prefix (CP) and flexibility of introducing well time-frequency localized pulse shapes. However, under dispersive channel condition, the intrinsic inter-symbol and inter-carrier interference arises in OFDM/OQAM system. Especially, the surrounding data symbols will cause interferences to the pilot symbols, leading to channel estimation error and degradation of system performance. In this paper, an efficient pilot structure and a channel estimation method are proposed for OFDM/OQAM system. The basic principal is to rebuild the transmitted symbols around the considered pilot position through pre-decision, then calculate and cancel the interference from the received signal. Analysis and simulation results show that the proposed scheme outperforms conventional ones with respect to both channel estimation accuracy and bit error rate (BER) performance while with less pilot consumption.

In this paper, we compare the performance between channel estimation based on compressed sensing (CS) and time-domain least square (LS) for single-carrier (SC) communication system. Unlike the conventional channel estimation techniques such as frequency domain LS which is used in the condition that the length of pilot sequence is equal to data sequence, the estimation scheme based on CS requires smaller length of pilot sequence. In this paper, the corresponding system structure is presented. Zadoff-Chu sequence is used to generate the pilot sequence, which is shown to perform better in forming measurement matrix of CS than pseudo random sequence. Simulation results demonstrate that channel estimation based on CS achieves a better bit error rate (BER) performance than time domain LS with a smaller pilot sequence and thus raising data rate of the SC communication system.

Orthogonal frequency division multiplex/offset QAM (OFDM/OQAM) has been proven to be a promising multi-carrier modulation (MCM) technique for the transmission of signals over multipath fading channels. However, OFDM/OQAM has also the intrinsic disadvantage of high peak-to-average-power ratio (PAPR) that should be alleviated. This paper focuses on the reduction of the clipping noise and out-of band radiation caused by the clipping process. The basic principle is to estimate the clipping noise and then eliminate it from the received signal. Analysis and simulation results show that, with one time iteration, the proposed method can effectively improve the bit error ratio (BER) performance.

Orthogonal frequency division multiplex/offset QAM (OFDM/OQAM) and N-continuous OFDM are both improved multi-carrier modulation (MCM) techniques for the transmission of signals over multipath fading channels. In this paper, we aim to compare these two techniques with respect to out-of-band radiation, bit error ratio (BER) and calculation complexity. Analysis and simulation results show that, compared to the N-continuous OFDM, the OFDM/OQAM has lower out-of-band radiation, calculation consumption and similar BER performance.

In this paper, a simple transmit diversity scheme using two transmitting and two receiving antennas for STBC structure is presented. Moreover, a detection algorithm with iterative interference cancellation for STBC-OFDM/OQAM system is proposed to improve bit error ratio performance. Simulation results prove that the proposed detection algorithm is an effective algorithm for STBC-OFDM/OQAM system.

In this paper, an effective preamble structure with only one zero-value guard symbols for OFDM/OQAM systems is proposed to improve spectrum efficiency. Moreover，a preamble interference cancellation (PIC) based channel estimation (CE) scheme is proposed to mitigate the residual ISI in OFDM/OQAM systems. Simulation results prove that the proposed preamble with PIC based channel estimation is an effective structure for OFDM/OQAM systems.