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This paper proposes a channel ranking based spreading factor optimization for orthogonal frequency division multiple interleave division multiple access (OFDM-IDMA) on visible light communication (VLC) systems. VLC is under the global spotlight, since light emitting diode (LED) has recently become a part of building infrastructure and its functionality is quite easy by implementing communication components to LED lighting. To enhance the VLC capability, OFDM-IDMA was previously proposed as a multiple access method. It also employs a spectrum spreading, in which the symbol is orthogonally spread to a specified number of subcarriers. Here, an interleave pattern specific to the transmission signal of each user can improve the separation capacity of the source signal and therefore multiple access becomes possible in VLC-OFDM-IDMA. However, it requires a lower rate error correction code and a large spread factor to limit the throughput performance. To resolve this problem, we introduce a new channel ranking and allocate an appropriate spreading factor to each user according to their channel state. Overall, BER performance and throughput performance can be enhanced by optimising the spread code.

This paper describes an attempt to develop extremely wideband multi-mode surface acoustic wave (MMS) filters in the gigahertz range. The Cu-grating/15 degrees YX-LiNbO3 (15-LN)-substrate structure is employed. First, a design tool developed for the present purpose is detailed. Precise simulation is performed using a modified coupling-of-modes model, in which the coupling between propagating surface and bulk acoustic waves is taken into account. Parameters necessary for the simulation are determined experimentally. Next, this simulation tool is used to design a wideband MMS filter employing pitch-modulated IDTs proposed by the authors. It is shown that a fractional bandwidth of more than 12% is achievable by successfully using six SAW resonances supported in the MMS structure. The designed MMS filter was fabricated on a Cu-grating/15-LN-substrate structure. The passband width of 12.6% and the minimum insertion loss of 1.2 dB were experimentally obtained around 850 MHz. The measured result was in good agreement with the simulation.

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This paper expands an analytical formulation of maximal ratio transmission (MRT) precoded massive multiple-input multiple-output (MIMO) systems. Evaluating performance on massive MIMO systems where both base station (BS) and user terminals (UTs) have array antennas could impose impractical computation complexity. The existing work derived the power distribution of inter-user interference (IUI) but that of the desired signal was treated as fixed. This paper enhances its modeling accuracy by deriving the latest. The consistency of the proposed model is confirmed by comparing it to the simulation results.