The packet error rate (PER) performance of space-time block code based multi-hop cooperative relaying is studied. In the case of multiple relays at each hop, a unique feature of the end-to-end PER performance can be observed up to 3rd hop. In this letter, an outdoor measurement campaign is conducted to verify this PER performance. In addition, a cooperative relaying scheme with received data sharing among relays is also examined. It is experimentally shown that PER at the 3rd hop is better than that of the 1st hop.
Generally, maximum Doppler frequency can be derived from velocity of moving vehicle. However, frequency shifts beyond the maximum Doppler frequency are observed in actual measurement. In this paper, Doppler shift is calculated in consideration with the shift caused by other moving vehicles. Numerical results show that the actual measured Doppler shift can be reproduced with high accuracy by considering the frequency shift at the other moving vehicles.
This letter proposes a frequency domain equalization (FDE) scheme with a threshold in molecular communication (MC). The responses of a MC channel are tendency to have low pass characteristics and inter-symbol interference limits the data rates of MC. However, because of the characteristics of the MC channel, equalization coefficients for high frequency components may increase. Therefore, noise enhancement occurs and it deteriorates communication performance. As large channel responses concentrate at around a zero-frequency component, in the proposed equalization scheme, the high frequency component of the received signal is eliminated if the equalization coefficient exceeds a threshold in the proposed scheme. Numerical results obtained through computer simulation show that the threshold improves the communication performance with the proposed FDE. It is also shown that the trade-off between the noise enhancement and the pulse waveform effects on the performance.
Mobile edge computing (MEC) has restricted computation resource and limited bandwidth resource when serving multiple users simultaneously. In general, a user’s task can not be always parallelized. In this paper, we study a joint computation and bandwidth resource allocation problem, considering a generalized task computing model. The computation capacity is modeled as a non-decreasing concave function about allocated computation resource, and the joint computation and bandwidth resources allocation problem is solved by cvx opt. framework. Simulation results show that our proposed scheme is greatly superior to the serial processing benchmark scheme for Non-linear model. With non-linear model, higher computational multiplexing gain can be achieved, however, for linear model, there is no gain that can be obtained from the proposed scheme.
We have been proposing a direct spectrum division transmission (DSDT) technique that can divide a single carrier signal into multiple sub-spectra and assign them to dispersed frequency resources of a satellite transponder to improve spectrum utilizing efficiency. This letter overviews the concept of DSDT and shows the results of feasibility verification on DSDT via satellite experiments. In a past study, we carried out fundamental satellite experiments on DSDT over a single transponder. This time, we conduct satellite experiments on DSDT over multiple transponders by using the latest DVB-S2X format signal. The BER performances of signals divided by the DSDT technique were almost the same as that of a single-carrier. We confirmed that DSDT was practical.
Radio propagation simulation is a valuable tool to predict the propagation channel characteristics for system design and service-cell planning. In the simulation, the accurate environment model is needed to improve the prediction accuracy of the site-specific channel. Recently, the ability of smartphones makes remarkable progress, and the point cloud data of the environment can be obtained by the video camera output of the smartphone. However, because of the memory size limitation of those devices, it is necessary to repeat the measurement and combine the several point cloud datasets to model the large-volume environment. In this paper, we proposed the color-based registration method by extending the fast descriptor algorithm. We applied our proposed algorithm to the point cloud data taken by the video camera of the smartphone, and proved that the calculation time was reduced by 70% in the office scenario. The work is expected to be utilized for the radio propagation simulation in actual environments.
We have proposed a transverse electromagnetic (TEM) horn antenna for radiated immunity tests in close proximity as specified in IEC 61000-4-39 and evaluated the main characteristics of the antenna required in the immunity tests. The TEM horn antenna has broadband radiation characteristics with a low VSWR and generates a homogeneous field over the entire test frequency range from 380 MHz to 6 GHz.
This paper proposes a scheme to resolve the imbalance state in a network in which flow types, mice and elephant flows, are considered. A combination of link utilized rate and transmission delay of each link are considered as a link cost. In the proposed scheme, the load imbalance state is resolved by dividing the elephant flow into several subflows and injecting each subflow into multiple paths. The maximum utilization rate of the proposed scheme decreases 38.9%, compared to a conventional scheme.