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Classic scheduling algorithms for the LTE uplink in the literature may cause severe packet loss, poor fairness, and inefficient resource allocation. To alleviate packet loss, delay budget rather than channel condition plays a key factor in our proposed algorithm that allows the user equipment (UE) with the least left delay budget to be scheduled first. Besides, the UEs with fewer allocated resources can be served earlier to improve fairness. For reaching efficient resource utilization, our proposed algorithm further poses a constraint in sequential resource allocation. Via extensive simulations, we successfully demonstrate that our proposed algorithm significantly outperforms the closely related algorithms in terms of packet loss ratio and fairness index at the cost of raised end-to-end delay but still within the delay bound. For our proposed algorithm, it also gains improvement in throughput due to its reduction in the packet loss ratio and bounded relaxation in the end-to-end delay.

Molecular communication has been considered an emerging technology for both scientific and engineering interests, due to molecular biology and the need for nano-scale communication and computation systems. Molecular communication systems are widely analogue to electrical communication systems involving emitting molecules, diffused propagation of molecules, and reception of molecules, under stochastic characteristics of relatively slow propagation speed and short transmission range. To facilitate large-scale molecular information systems for the purpose of communication and computation, state-of-the-art explorations are generally assumed perfect alignment of timing among molecular devices and sub-systems. To reach synchronous condition in electronics, phase locked loop (PLL) is known to align timing or phase of waveforms. We extend PLL into molecular PLL (MPLL) consisting of basic elements such as molecular phase detector, molecular loop filter, and molecular voltage controlled oscillator. Due to stochastic nature of molecular diffusion, we further analyze MPLL in terms of the diffusion jitter, displacement, and the (particle or molecular) counting noise. Simulations verify the MPLL concept model, tracking performance, and robustness in operation.

The issues of frequency offset and channel estimation are considered for the downlink of coordinated multiple-input multiple-output orthogonal frequency-division multiplexing systems. Multiple carrier frequency offsets exist in this coordinated system. Without implementing an appropriate compensation for these offsets, both inter-carrier and inter-cell interference will degrade the system performance. Here, we adopt a parallel interference cancelation strategy to iteratively mitigate inter-cell interference, and propose a frequency offset estimator, approximated by a Hadamard product and a Taylor series expansion, to eliminate the inter-carrier interference. Our scheme is significantly less complex than existing methods. Furthermore, the proposed channel estimator is robust to frequency offsets and performs comparably well to these conventional approaches.

In this paper, we reconsider the issues of frequency offset and channel estimation in multiple-input-multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. We first design “cascaded orthogonal” pilot symbols and adopt the properties of Fourier transform and Hadamard product to deliver a closed-form estimate of frequency offset; meanwhile, another closed-form estimate of channel under minimum mean square error (MSE) criterion is presented. A tight lower bound for the MSE of the channel is also derived. The proposed channel estimator is robust to the residual frequency offset, whereas the frequency offset estimator is nearly independent of the unknown channel vector and is also robust to channel variations. Simulation results show that the proposed method greatly reduces the MSE of the channel in the moderate-to-high value of signal-to-noise ratio (SNR), even at a large normalized (by subcarrier spacing) frequency offset |ν| = 0.5. Compared with the optimal pilot design without frequency offset, our solution performs only slightly worse for low values of frequency offset (|ν| ≤ 0.01), but the difference is insignificant. The computational complexity of the proposed scheme is also much lower than that of the conventional iterative means.

This paper reexamines the problem of frequency offset estimation and signal detection of the Bell laboratories layered space-time (BLAST) scheme. Today, typical multiple-input-multiple-output (MIMO) receivers separately execute these two steps, but in succession. In this paper, we propose a joint frequency offset estimator and signal detector (JFESD). In our scheme, the frequency offset can be well compensated by utilizing the intermediate detector results. Our detector is evolved from conventional zero-forcing BLAST detectors. It is extendable to situations where the receive dimension is lower than the transmit dimension with a marginal increase of computational complexity. We evaluate the bit error probability and mean square error performance of the JFESD and compare them with other schemes.