In this paper, we investigate the problem of a wide-gap frequency hopping sequence (WGFHS) in a cognitive frequency hopping (CFH) system. The CFH system can achieve more reliable communication in a complex electromagnetic environment than does a conventional frequency hopping (FH) system. Moreover, an appropriate WGFHS could minimize the impact of jamming on the CFH system. However, conventional WGFHS adopted in the CFH system performs poorly in statistical properties and FH synchronization. Therefore, we propose an algorithm called the classified pseudorandom perturbation (CPRP) that can generate a random and uniform WGFHS with its uniform distribution keeping invariable during wide-gap mapping. In addition, it can achieve a high FH synchronization probability because all of the required parameters can be obtained from the known real-time status and sensing results. The simulation results indicate that the WGFHS generated by the CPRP outperforms the existing WGFHSs, such as the Reed–Solomon (RS) code with dual subbands (DSBs) and the chaotic sequences with shifting replacement.

Generation and Characteristics Analysis of Cognitive-Based High-Performance Wide-Gap FH Sequences

Massive multi input multi output orthogonal frequency division multiplexing (MIMO-OFDM) systems are progressively improving the current wireless communication standards towards 5G, due to their high data rates. The channel estimator (CE) employed in these systems is based on 2D-grid type pilot arrangement, which offers better spectral efficiency. The 2D arrangement requires the CE to incorporate a time interpolator (TI) in addition to the usual frequency interpolator (FI). The prime concerns for a TI in massive systems are minimal storage, low computational complexity, and system reliability. The existing low-pass FI or a linear FI can serve as TI; however, each of them does not address all the prime concerns in totality. In this paper, a discrete Fourier transform (DFT) based TI is introduced with three distinguished features; minimum storage space similar to a linear TI, computational complexity at par with linear TI, and improved system reliability compared to low-pass TI. Using system bit error rate (BER) simulations in various Rayleigh fading channels characterized by U-shaped Doppler spectrum, it is verified that the proposed CE incorporating the DFT-based TI indeed provides better system reliability with minimal storage and low computational complexity.

A pilot aided channel estimator using DFT based time interpolator for massive MIMO-OFDM systems

In a frequency-hopping (FH) system, to avoid that the received signal would be prone to be interfered, the equipped FH sequence of each user should have wide FH gap, i.e., the adjacent two frequencies should have some gap. In this letter, we extend the Lempel–Greenberger bound and Peng-Fan bounds for wide-gap frequency-hopping sequences (WGFHSs). The proposed bounds are tight in the sense that they can be achieved by the parameters of some WGFHSs.

New Bounds on Wide-Gap Frequency-Hopping Sequences

Channel estimation is crucial for modern WiFi system and becomes more and more challenging with the growth of user throughput in multiple input multiple output configuration. Plenty of literature spends great efforts in improving the estimation accuracy, while the interpolation schemes are overlooked. To deal with this challenge, we exploit the super-resolution image recovery scheme to model the non-linear interpolation mechanisms without pre-assumed channel characteristics in this paper. To make it more practical, we offline generate numerical channel coefficients according to the statistical channel models to train the neural networks, and directly apply them in some practical WiFi prototype systems. As shown in this paper, the proposed super-resolution based channel estimation scheme can outperform the conventional approaches in both LOS and NLOS scenarios, which we believe can significantly change the current channel estimation method in the near future.

Channel Estimation for WiFi Prototype Systems with Super-Resolution Image Recovery

In frequency hopping (FH) communication systems, frequency hopping sequences (FHSs) are crucial in determining the system’s anti-jamming performance. If FHSs can ensure a wide-gap between two adjacent frequency points to avoid the frequency points with high interference probability, it will significantly improve the FH communication system’s anti-interference ability. Moreover, if each frequency point appears at the same number of times in a sequence period, the system’s anti-electromagnetic interference will be enhanced. Therefore, it is desirable to employ FHSs with low Hamming autocorrelation, wide frequency-hopping gap, and good uniformity in practical applications. However, to the best of our knowledge, no such infinite classes of FHSs have been reported in the literature to date. This paper aims to present two constructions of uniform wide-gap frequency-hopping sequences (WGFHSs) by concatenating two or three adequately designed sequences. For the first time, we obtain two infinite classes of WGFHSs, which are optimal with respect to the well-known Lempel-Greenberger bound. 

Constructions of Optimal Uniform Wide-Gap Frequency-Hopping Sequences

For FH systems, the frequency hopping sequences should be designed to be a wide interval which can better enhance the capability of system for anti-interference. This paper presented an improved generate method on FH sequence with given minimum gap — mod d plus remainder algorithm. We conducted some simulations using MATLAB, with the traditional dual-band method were compared with balance coefficient, the average gap and average gap rate of FH and auto-correlation. The simulation results show that the new improved method is superior to the traditional dual-band method.

http://ieeexplore.ieee.org/iel5/5492939/5524731/05524961.pdf

Design and performance analysis of frequency hopping sequences with given minimum gap

This paper discussed the channel estimation method of OFDM for DVB-T systems, and presents a two-dimensional time-frequency interpolation channel estimation scheme. This scheme, which uses Linear interpolation algorithm and Laplace interpolation algorithm, is based on the distribution of discrete pilot frequency of DVB-T. Results from computer simulations of OFDM transmission for DVB-T systems employing the new scheme showed that it possess better bit error rate performance than the single dimension interpolation method

Two-dimension interpolation for OFDM channel estimation of DVB-T systems

In DVB-T standard, OFDM was recommended to improve the ability of anti-interference of multiple path and system spectral efficiency. In order to demodulate OFDM signals accurately, channel estimation is needed for received signals. In this paper, the channel estimation method based on pilot is discussed for DVB-T system, and a new two-dimensional time-frequency interpolation channel estimation approach is proposed. Which using linear interpolation in the time-domain, and using Gaussian interpolation in the frequency-domain. The paper presents bit error rate performance generated from computer simulations. The simulation results show that the two-dimension interpolation approach possesses better performance than the single dimension interpolation method.

The Channel Estimation of OFDM System Based on DVB-T

In this paper, an improved generate method on FH sequence with given minimum gap is proposed — mod d plus remainder algorithm. We conducted some simulations using MATLAB, with the traditional dual-band method were compared with balance coefficient, the average gap of frequency hogging, the average gap rate of frequency hopping and autocorrelation. The Simulation results show that the new improved method is superior to the traditional dual-band method.

Frequency hopping sequences with given minimum gap

Bit-Interleaved Code Modulation with iterative decoding(BICM-ID) is a technique with combination of coding and high-order modulation.The application of this method can improve system bandwidth utilization continually in order to better approach the system's capacity.In order to improve the system bandwidth efficiency more effectively,Multi-Dimensional(MD) labeling map modulation can be used in the BICM-ID system.Based on the analysis to the pairs of error probability(PEP) of MD mapping,the optimal constructing methods of Four-Dimensional mapping of the QPSK and 8-PSK are introduced and the simulation to their performance is presented.

Zhang Huaqing

Papers

Design and performance analysis of frequency hopping sequences with given minimum gap

Two-dimension interpolation for OFDM channel estimation of DVB-T systems

The Channel Estimation of OFDM System Based on DVB-T

Frequency hopping sequences with given minimum gap

Constellation Mapping of MD in BICM-ID