We investigate the degrees of freedom (DoF) of a coexisting network composed by two interfering basic 2 × 2 X channels with single antenna at each node. Asymptotic interference alignment approach is used to obtain the lower bound on the based on symbol extension model. When n tends to infinity, the DoF lower bound achieves 2, which is proven to be the upper bound on DoF. Therefore, the bound on DoF is tight.

The Common Public Radio Interface (CPRI) and 10 Gbps Ethernet are the promising solution for connecting the baseband unit (BBU) and the remote antenna unit (RAU) of the Long-Term Evolution (LTE) system. It is also capable of deploying the radio cell at the indoor location. Since the CPRI link is based on the point-to-point link, the handover process occurs whenever the mobile user moves across the cell. Handover is more increased than outdoor location due to the limitation of transmitting power of the indoor equipment. In this paper, in order to reduce the handover, the Radio over Fiber (RoF) link is introduced instead of the point-to-point link. And the optical matrix switch controls to combine multiple cells into one cell. Simulation results show that the proposal reduces the number of handover by 38.27% compared to point-to-point based network.

This paper demonstrates signal light carrier automatic pull-in and phase-lock to an optical frequency comb reference by our newly developed microcomputer-assisted phase-lock loop circuit. The microcomputer utilizes a binary-search algorithm to alter the oscillation frequency of the slave laser and achieve rapid pull-in to the master laser. It achieves automatic phase-locking time of 0.45 msec when the laser-diode frequency lies within the pull-in range of ±100 MHz. The single side band phase noise is just 1.8° at offset frequencies from 10 Hz to 5 MHz. This phase noise value is not expected to cause any power penalty with QPSK modulation.

We describe a method for measuring optical pulse broadening with continuous wave beam emitted from a low-coherence source. A two-beam interferometer composed of nondispersive and dispersive arms makes it possible to obtain the dispersion-induced pulse broadening. Experiments are carried out using a standard single-mode fiber and a two-mode fiber in the 1560 nm-wavelength region. As a result, the square of the degree of coherence, |γ|², well reflects the dispersion-induced pulse broadening for an unchirped Gaussian pulse. The theoretically derived relationship between these two physical phenomena well reflects the experimentally obtained results. Chromatic dispersion values obtained by the method are in good agreement with those obtained by the alternative method. The salient feature of the present method is clearly shown.

We numerically evaluate optical transmission characteristics of four- and eight-dimensional modulation formats, and find that they are effectively improved by wavelength-diversity or cross-talk (XT) compensation with 4 × 4 adaptive multiple-input multiple-output (MIMO) equalization. Further, we quantitatively verify that the four-dimensional formats with the diversity configuration is superior to the eight-dimensional formats using dual carriers in terms of the robustness against unbalanced OSNR of the two carriers. We also quantitatively demonstrate the XT compensation effectiveness for the eight-dimensional modulation formats in case that the dual carrier spacing is less than the symbol rate.

In this paper, under square quadrature amplitude modulation (QAM) constellation and Nakagami-m fading channel assumptions, the bit error rate (BER) of the data transmission in an embedded fingerprint physical (PHY) layer authentication system is derived in a closed-form, and the correctness is validated by simulations. Analytical results show that the impact of the authentication tags on the data BER is substantial when the modulation orders are high. The signal to noise ratio (SNR) loss caused by the tags is also given in a closed-form, which turns out to be increasing with both modulation orders and the fading severity m.