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A heterogeneous wireless IoT system is assumed to be used where several wireless subsystems with different standards using the same frequency coexist in a narrow space such as a factory. In the heterogeneous wireless IoT system, interference from the micro-cell system (µSystem) to the pico-cell system (pSystem) decreases the pSystem throughput. In this paper, we propose a Dual Clear to Send (Dual-CTS) method as a novel access control method for avoiding interference by exploiting spatial resources. In the proposed Dual-CTS method, µSystem gateway (µGW) does not broadcast only conventional CTS but also special CTS for pNode (pCTS) after receiving Require to Send (RTS). The pCTS enables pNode to transmit data using the same time and the same frequency resources as µNode uses. Calculation and simulation results show that the pSystem throughput in the proposed method is higher than one of the conventional methods by 1.3 times or more by exploiting the spatial resource.

The hidden terminal problem degrades the uplink system throughput of wireless local area network seriously. In this paper, we propose the optimum allocation (OA) scheme of the location-based virtual sector (VS) method, which solves the hidden terminal problem without massive overheads like request-to-send and clear-to-send (RTS/CTS) packets. The VS method forms sectors virtually to make short-distance mobile terminal (MT) groups using MTs’ location information. In the group, all MTs can sense the transmission of all other MTs. In the proposed method, rough time slot control is implemented for intersector control, which does not need a highly functional centralized controller. The proposal OA scheme of the VS method improves the fairness among MTs by optimizing active periods of VS according to the number of MTs in each VS. By computer simulations, we show that the proposed method can increase the system throughput from the RTS/CTS and improve fairness among MTs even in the condition that positioning error is 1/10 of cell radius.

Millimeter-wave (mmW) wireless body area network (WBAN) is effective as one of the methods to reduce inter-WBAN interference even in user-dense conditions because of human body blocking. In this paper, we evaluate intra-WBAN channel capacities in user-dense situation considering the inter-WBAN interference model by using elliptic cylinder approximation of the human body. We obtain the result that the intra-WBAN channel capacity of over 50 Mbit/s at cumulative distribution function (CDF) of 0.1 was ensured with the system bandwidth of 100 MHz, even in the case of a high user density of 200 users/100m2 by the computer simulation.

Wireless body area network (WBAN)using millimeter wave (mmW)is expected to reduce inter-WBAN interference because of large attenuation, however it is necessary to consider the connectivity of the mmW intra-WBAN communication. We have proposed the toe-hop mmW WBAN in the walking pause and measured on-body propagation losses at 60 GHz. In this paper, we evaluate a channel capacity to show the reliability of the proposed method. Monte carlo simulation shows that the proposed method can ensure the channel capacity of 10 Mbit/s with a probability of more than 99.6% in a walking situation.

We propose the traffic navigation & relay to shorten transmission delay time of the conventional delayed offloading method which is a load balancing scheme of heterogeneous wireless networks. In the original traffic navigation which is a kind of delayed offloading method, the sender user equipment (UE) moves the route that the UE achieves the highest throughput, but transmission delay time is one of the main issues. The proposed traffic navigation & relay can reduce transmission delay time to entrust the packets to other UEs (relayer UEs) if the relayer UEs are able to reach the small cell faster than the sender UE. It was evaluated by computer simulation that the proposed traffic navigation & relay improves the UE’s cumulative distribution function (CDF) of transmission completion time by 42 percentage points at 600 s from the conventional method when the density is 125 UEs/km2.

In this paper, we investigate the link level performance considering the influence of the error vector magnitude (EVM) of a transmit signal in a downlink non-orthogonal multiple access (NOMA) with two users. The motivation of this work is that to clarify the impact of the distortion of the transmit signal, which is expressed as the EVM, on the reception performance of each user equipment (UE). Results show that the performance of the near-base-station UE, which implements a successive interference cancellation (SIC), is deteriorated as the EVM increases, and that the amount of the deterioration rapidly increases as the modulation level is higher. In contrast, the performance of the far-base-station UE, which does not implement the SIC, is less affected even with the large EVM. Furthermore, we also show that the downlink NOMA requires lower EVM values than the downlink orthogonal multiple access (OMA), when comparing them at the same modulation level. Accordingly, a high quality radio frequency (RF) transmitter will be required for the introduction of NOMA to the next generation mobile communication systems.

Wireless body area network (WBAN) using millimeter wave is expected to reduce inter-Wbaninterference, but it is necessary to consider the connectivity of the millimeter wave intra-Wbancommunication. In this paper, we propose the directional millimeter-wave WBAN in the walking pause considering directional selectivity between intra-Wbancommunication and inter-Wbaninterference. The measurements of on-body propagation loss are shown at 60 GHz comparing with geometrical line-of-sight (LoS) experimentation using a flashlight for directional millimeter-wave WBAN. From the measurements result, there is no severe problem due to the body attenuation of intra-Wbancommunication with the directional antenna for Tx and Rx antennas.

Wireless body area network (WBAN) using millimeter wave is expected to suppress inter-WBAN interference in crowded condition because higher free space loss and higher human body attenuation than that of microwave such as 2.4 GHz reduce interference power. The environment with lots of people makes the probability of human body blocking of the interference path high. In this paper, two kinds of human body attenuation are measured to evaluate the power of inter-WBAN interference at 60 GHz: One is the body attenuation who wears Rx antenna and the other is the body attenuation who exists between Tx and Rx antennas. From the result, assuming in general WBAN condition, interference power of inter-WBAN is under the received power sensitivity in most cases when Tx antenna and Rx antenna are non-line-of-sight (NLoS).