Shengmei Zhao

Polar codes and its application in speech communication

Polar codes are a class of codes proposed currently, which can achieve the capacity of binary symmetric channel with low encoding and decoding algorithm. However, its application is less discussed in the literature. In this paper, we discuss the application of Polar codes in speech communication, and compare the performance of systems with that of low density parity check (LDPC) codes both in Additive white Gaussian channel and Rayleigh channel. The numerical results show that the system coded by Polar codes has a better performance than that coded by LDPC codes, and the system is good with lower code rate and longer code length.

Turbulence mitigation scheme based on multiple-user detection in an orbital–angular-momentum multiplexed system*

Atmospheric turbulence (AT) induced crosstalk can significantly impair the performance of a free-space optical (FSO) communication link using orbital angular momentum (OAM) multiplexing. In this paper, we propose a multiple-user detection (MUD) turbulence mitigation scheme in an OAM-multiplexed FSO communication link. First, we present a MUD equivalent communication model for an OAM-multiplexed FSO communication link under AT. In the equivalent model, each input bit stream represents one users information. The deformed OAM spatial modes caused by AT, instead of the pure OAM spatial modes, are used as information carriers, and the overlapping between the deformed OAM spatial modes are computed as the correlation coefficients between the users. Then, we present a turbulence mitigation scheme based on MUD idea to enhance AT tolerance of the OAM-multiplexed FSO communication link. In the proposed scheme, the crosstalk caused by AT is used as a useful component to deduce users information. The numerical results show that the performance of the OAM-multiplexed communication link has greatly improved by the proposed scheme. When the turbulence strength is 1 × 10−15 m−2/3, the transmission distance is 1000 m and the channel signal-to-noise ratio (SNR) is 26 dB, the bit-error-rate (BER) performance of four spatial multiplexed OAM modes lm = +1,+2,+3,+4 are all close to 10−5, and there is a 2–3 fold increase in the BER performance in comparison with those results without the proposed scheme. In addition, the proposed scheme is more effective for an OAM-multiplexed FSO communication link with a larger OAM mode topological charge interval. The proposed scheme is a promising direction for compensating the interference caused by AT in the OAM-multiplexed FSO communication link.

Quantum multi-user detection scheme with Discrete coherent states approximation

Multi-user detection (MUD) techniques will be adopted in the future wired and wireless communication system. It is known that quantum detection techniques promise efficient optimal solutions to this NP (non-polynomial) hard problem in classical domain. Discrete coherent state(DCS) approximation method is a practical model for solving the mixed-state detection problem. In this paper, we use DCS approximation model for the MUD problem. For a noisy quantum channel, it is feasible to consider the output states are mixed states, which are the input pure states corrupted by the noise when the pure states pass thought the noisy quantum channel. For simplicity and generality, we deduce the error probability of symbol against correlation coefficient in two users fashion. By numerical simulations, we analyze and compare the performance of this representation. The simulation results show that the detection error will increase while the correlation coefficient increase, and the performance is also effected by the noise level. With less noise, the system will get better performance. The DCS approximation representation is a good detection scheme for quantum multi-user detection.

Plug-and-play round-robin differential phase-shift quantum key distribution

The round-robin differential-phase-shift quantum key distribution (RRDPS-QKD) protocol could provide an effective way to estimate the leakage information without monitoring the signal disturbance. Moreover, the self-compensating property of plug-and-play (P&P) setup can eliminate the variations of phase or polarization in QKD procedure. In the paper, we introduce the P&P concept into RRDPS-QKD, and propose a QKD protocol, named P&P RRDPS-QKD protocol, to make the RRDPS-QKD scheme more practical. We analyze the security, and discuss the key generation rate with infinite-intensity decoy state method. The results show that the proposed protocol is a good solution to RRDPS-QKD protocol with untrusted sources. It has a high security and its key generation rate could be as good as the protocol with trusted sources when the average input photon number N is greater than 106. In addition, the proposed protocol has a high noise tolerance in comparison with P&P BB84-QKD protocol.

Quantization and reliability-aware iterative majority-logic decoding algorithm for LDPC code in TLC NAND flash memory

Multi-level per cell (MLC) /Triple-Level per cell (TLC) technique significantly improves storage density with low cost increases, which stores more than one bit per cell, but also drastically decreases reliability in NAND flash memory. As the bit number per cell increases, correspondingly cell-to-cell interference (CCI) becomes the major challenge for NAND flash memory technology scaling. Recently, low-density parity-check (LDPC) code is considered as the most appropriate scheme of next generation Error Correcting Code (ECC) in NAND flash memory. In this paper, by exploiting the intra-cell characteristics in TLC NAND flash memory channels, a low-complexity quantization and reliability-Aware iterative majority-logic decoding (QR-IMLGD) algorithm for LDPC code is proposed to reduce the memory read latency and effectively improve the throughput of LDPC decoding. The proposed algorithm takes advantage of highly unequal error probability of input log-likelihood-ratios (LLRs) in the same cells, employ small bit-level quantizer and update only less reliable variable nodes that are initiated with higher error probability LLR values. Simulation results show that the proposed QR-IMLGD algorithm can yield a noticeable improvement in decoding convergence rate without compromising the error performance in TLC NAND flash memory channels.

Turbulence mitigation with MIMO equalization for orbital angular momentum multiplexing communication

Atmospheric turbulence (AT) induced crosstalk can significantly impair performance of free-space optical (FSO) communication link using orbital angular momentum (OAM) multiplexing. OAM-multiplexed communication is equivalent to the Multiple-input Multiple-output(MIMO) system. And MIMO equalization is a good method to mitigate the crosstalk existing in MIMO system. Based on the reason above, we propose a MIMO equalization turbulence mitigation scheme in an OAM-multiplexed FSO communication link. The numerical simulation results show that MIMO equalization mitigation method can mitigate the effects of AT. The Quaternary Phase Shift Keying (QPSK) signal constellation and bit-error ratio(BER) performances are analyzed.

A class of quantum irregular LDPC codes constructed from difference family

Making use of the advantage of classical irregular LDPC codes from difference family, a new construction of quantum irregular LDPC codes is proposed in this paper. The quantum parity-check matrix we constructed satisfies the requirement of dual-containing quantum CSS codes. The simulation result shows that the quantum irregular LDPC codes can perform better than the quantum regular LDPC codes with the similar parameter.

Two-dimensional multiplexing scheme both with ring radius and topological charge of perfect optical vortex beam

ABSTRACT Perfect optical vortex (POV) beam is a special kind of vortex beam, whose radius is independent of its topological charge. In this paper, we propose a two-dimensional multiplexing scheme with a ring radius and topological charge of POV beam. A communication system using the proposed multiplexing scheme with a two-step detection method is presented, and on–off keying modulation is applied to demonstrate the bit error rate (BER) performance under atmospheric turbulence. The numerical results show that the BER performance of the proposed scheme is better than that when only topological charge is multiplexed with the same conditions. The two-dimensional multiplexing scheme has an anti-interference capability since the ring radius is only concerned in magnitude. At the same time, the capacity and the spectral efficiency of the system are improved since both ring radial and topological charge of POV beam are used.

Bell’s inequality tests via correlated diffraction of high-dimensional position-entangled two-photon states

Bell inequality testing, a well-established method to demonstrate quantum non-locality between remote two-partite entangled systems, is playing an important role in the field of quantum information. The extension to high-dimensional entangled systems, using the so-called Bell-CGLMP inequality, points the way in measuring joint probabilities, the kernel block to construct high dimensional Bell inequalities. Here we show that in theory the joint probability of a two-partite system entangled in a Hilbert space can be measured by choosing a set of basis vectors in its dual space that are related by a Fourier transformation. We next propose an experimental scheme to generate a high-dimensional position-entangled two-photon state aided by a combination of a multiple-slit and a 4 f system, and describe a method to test Bell’s inequality using correlated diffraction. Finally, we discuss in detail consequences of such Bell-test violations and experimental requirements.

Reconciliation of continuous variable QKD using Gaussian post-selection and systematic Polar code

The transmission distance of continuous variable QKD (CV QKD) protocol based on Gaussian modulation has been quite limited by the low efficient reconciliation protocol. On the other hand, noiseless linear amplifier (NLA) have greatly enhanced the ability of CV QKD. In this paper, we propose a Gaussian post-selection method simulating NAL in CV QKD, followed by a reconciliation process based on systematic Polar code. We distill the reliable data through the post-selection filter as the raw key and then encode them with systematic polar code. The numerical simulation show that the secure transmission distance can be enlarged more than thirty kilometers while keeping the advantages of Gaussian security evidences. The key error rate can close to zero when signal-to-noise ratio (SNR) is near 3 dB.