The combination of Multiple-Input Multiple-Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) technologies gives wireless communications systems the advantages of lower bit error rate (BER) and higher data rate in frequency-selective fading environments. However, the main drawbacks of MIMO systems are their high complexity and high cost. Therefore, antenna selection in MIMO systems has been shown to be an effective way to overcome the drawbacks. In this paper, we propose two receive antenna selection methods for a MIMO-OFDM system with radio frequency (RF) switches and polarization antenna elements at the receiver side, taking into consideration low computational complexity. The first method selects a set of polarization antenna elements which gives lower correlation between received signals and larger received signal power, thus achieves a lower BER with low computational complexity. The second method first selects a set of polarization antenna elements based on the criterion of the first method and another set of polarization antenna elements based on the criterion of minimizing the correlation between the received signals; it then calculates the signal-to-interference-plus-noise power ratio (SINR) of the two sets and selects a set with larger SINR. As a result, the second method achieves a better BER than the first one but it also requires higher computational complexity than the first one. We use the measured channel data to evaluate the performance of the two methods and show that they work effectively for the realistic channel.

This paper proposes a novel M-ary FSK demodulation scheme using the Short Time Discrete Fourier Transform (ST-DFT) analysis named Frequency Sequence Estimation (FSE) for low earth orbit (LEO) satellite-based personal multimedia communications. The FSE is a kind of the Viterbi algorithm, searching for the maximum likely frequency path using the instantaneous ST-DFT output as a metric. It is based on the fact that the discrete time-frequency representation of the received signal can be interpreted as a trellis diagram. The proposed method has the excellent transmission performance and spectral efficiency, as well as its own hardware simplicity and frequency offset insensitivity.

This paper demonstrates 300GHz terahertz wireless communication using CMOS transmitter (TX) and receiver (RX) modules targeting sixth-generation (6G). To extend communication distance, CMOS modules with WR-3.4 waveguide interface and a high-gain antenna of 40dBi Cassegrain antenna are designed, achieving 36Gbps throughput at a 1m communication distance. Besides, in order to support orthogonal frequency-division multiplexing (OFDM), a self-heterodyne architecture is introduced, which effectively cancels the phase noise in multi-carrier modulation. As a proof-of-concept (PoC), the paper successfully demonstrates real-time video transfer at a 10m communication distance using fifth-generation (5G) based OFDM at the 300GHz frequency band.

This paper presents time slot assignment algorithms applicable to uplink of space division multiple access (SDMA)/time division multiple access (TDMA) systems with adaptive antennas. In the time slot assignment process for a new terminal in a cell, we consider not only the signal quality of the new terminal but also that of active terminals in the same cell. Intra-cell hand over is performed for an active terminal when its signal quality deteriorates. We evaluate the blocking and forced termination probabilities for pure TDMA systems, sectorized systems, and SDMA/TDMA systems in cellular environments by computer simulations. The simulation results show that the SDMA/TDMA systems have much better performance than the pure TDMA and sectorized systems.

In this paper, we evaluate the performance of single- and multi-antenna multi-carrier code division multiple access (MC-CDMA) downlink (base station to mobile terminal) systems in single- and multi-cell environments. We first propose a minimum mean square error (MMSE) filter with a Gaussian approximation for a single input single output (SISO) MC-CDMA downlink system. Then, we apply it to a SIMO (single input multiple output) system with a conventional turbo coding. Furthermore, we compare the performance of SISO (11) and SIMO (12) MC-CDMA systems with that of a multiple input multiple output (MIMO) (22) system employing space-time turbo coded modulation (STTuCM) in a multi-cell environment with 7 cells by computer simulation. Based on the computer simulation results, it is found that the considered MIMO system can achieve twofold capacity with the same transmission power in the multi-cell environment.

For an indoor area where a target node is tracked with anchor nodes, we can calculate the priori probability density functions (pdfs) on the distances between the target and anchor nodes by using its shape, three-dimensional sizes and anchor nodes locations. We call it “the area layout information (ALI)” and apply it for two indoor target tracking methods with received signal strength indication (RSSI) assuming a square location estimation area. First, we introduce the ALI to a target tracking method which tracks a target using the weighted sum of its past-to-present locations by a simple infinite impulse response (IIR) low pass filter. Second, we show that the ALI is applicable to a target tracking method with a particle filter where the motion of the target is nonlinearly modelled. The performances of the two tracking methods are evaluated by not only computer simulations but also experiments. The results demonstrate that the use of ALI can successfully improve the location estimation performance of both target tracking methods, without huge increase of computational complexity.

In order to construct a high-capacity and high-reliable indoor wireless communications system, it is essential to design the modulation/demodulation, coding and access schemes with high and variable data rate transmission capabilities, which meet the technical requirements inherent to wireless communications, i.e., high frequency utilization efficiency and robustness for fading. In this paper, we propose the frequency and time division multiple access with demand-assignment (FTDMA/DA) using multicarrier modulation as a frequency and time synchronous answer to meet the requirements, and analyze the performance of the FTDMA/DA system, taking account of teletraffic characteristics of multimedia information sources.