Contact resistance is an important parameter to evaluate the feasibility of carbon nanotubes (CNT) field-effect transistors (FETs) in high performance logic applications. In this paper we make the systematic study of contact resistance of solution-processed CNT-FETs by transmission line method (TLM) and the Y-function method (YFM). TLM needs to calculate the voltage between source and drain electrodes of a group of devices with different channel length, but YLM only needs the transfer characteristic curve of a single device. The results by our calculation indicate that, the resistance obtained by YFM is larger than that obtained by TLM, which provides reference value for the selection of methods to find contact resistance in the future.
In this paper, an unsupervised clustering algorithm based on the Gaussian Mixture Model (UCGMM algorithm) for the coherent optical OFDM communication system is proposed to determine the constellation diagram. The purpose of nonlinear equalization of communication systems is achieved. In a back to back transmission system, compared to the Kmeans algorithm and the without any clustering algorithm, the UCGMM algorithm can obtain gains of approximately 0.6dB and 2dB respectively. For the cases of simulation in optical fiber transmission, the transmission distance of UCGMM algorithm is extended by 45km relative to the K-means algorithm, and 75km relative to without any clustering algorithm. In both cases, the effectiveness of the proposed UCGMM algorithm in nonlinear equilibrium is proved.
In this paper, Radio over Fiber (RoF) system of generalized frequency division multiplexing (GFDM) and orthogonal frequency division multiplexing (OFDM) based on geometric shaping (GS) 16QAM is established on MATLAB and Optisystem platform. The transmission signals consist of a GFDM signal and a OFDM signal with bandwidth of 5GHz and 2.5GHz respectively. The frequency interval between the two signals is 10GHz. They were then transmitted onto carriers with a frequency of 60GHz by a quadrature modulator, the central frequencies of the two signals are 60GHz, 70GHz respectively. The transmission distance through single mode fiber (SMF) is 16km. Furthermore, we study the bit error rate performance of the proposed scheme combined with low density parity check (LDPC) codes. In the end of the paper, we analyze the performance of the proposed RoF system and be verified through MATLAB and Optisystem joint simulation that the proposed GFDM scheme with LDPC-GS-16QAM outperforms GFDM scheme with regular 16QAM by at least 15.3dB at bit error rate (BER) of 10−5 .
A non-uniform QAM OFDM modulation system based on probabilistic shaping (PS) and geometric shaping (GS) is proposed in this paper, which can effectively resist the interference among signal waveforms and improve spectrum utilization and channel capacity. First, Huffman coding is used in the scheme for probability shaping to reduce the average energy of the signal. Uniform 16QAM is adjusted to non-uniform 12QAM and uniform 32QAM is adjusted to non-uniform 12QAM. Then geometric shaping is applied. Taking generalized mutual information (GMI) as the objective function, pairwise optimization (PO) algorithm is applied to continuously adjust the constellation. Finally, the coordinate point with the largest mutual information is obtained. The simulation results show the performance of non-uniform 12QAM and non-uniform 24QAM under different conditions, we obtain the signal-to-noise ratio (SNR) with generalized mutual information curve, signal-to-noise ratio with bit error rate (BER) curve under different QAM modulation formats and the bit error rate with the different length of the fiber under different transmission modes. The results show that the proposed non-uniform 12QAM-GS-OFDM has a gain of 0.02 bit/symbol over 12QAM-OFDM, the proposed non-uniform 24QAM-GS-OFDM has a gain of 0.02 bit/symbol over 24QAM-OFDM.
A probabilistic shaping 64QAM scheme based on multilevel coded modulation is proposed, which combines the advantages of multilevel coded modulation and probabilistic shaping. The scheme combines several encoders with common rates through multilevel coded modulation. It can realize codewords with multiple code rates and save cost effectively. A simulation system is established to verify the performance of the proposed scheme. The results show that the proposed scheme requires lower SNR under the same BER while achieving higher code rate.
A Probabilistic Shaping (PS) 12-QAM scheme based on Set-Partitioned (SP) Two-Polarization (TP) is proposed to improve the effectiveness and reliability of Probabilistic Shaping 12-QAM (PS-12QAM). In this scheme, the Uniform 12- QAM constellation points are divided into two set partitions, and two polarization states are used to broaden the dimension between two set partitions. Moreover, the system capacity is further approached to Shannon limit by Probabilistic Shaping. The simulations on PS-8QAM, PS-12QAM, PS-16QAM and Probabilistic Shaping Set-Partitioned Two-Polarization 12- QAM (PS-SP-TP-12QAM) have been completed. The results show that, compared with PS-12QAM, the Euclidean distance between adjacent constellation points in PS-SP-TP-12QAM scheme is significantly optimized, and the bit error rate (BER) of this scheme is greatly improved up to 0.5dB. Compared with PS-8QAM and PS-16QAM, it brings a better balance between effectiveness and reliability performance.