In this paper, an enhanced feathery receiver initiated transmission (eF-RIT) protocol is proposed for wireless smart utility network (Wi-SUN) systems with high traffic bi-directional communications such as emergency gas automatic meter infrastructure (AMI) cases. Firstly, we evaluate the conventional F-RIT protocol by simulation and experiment. The measurement results show that the IEEE 802.15.4e compliant conventional F-RIT protocol can achieve over 90% transmission success rates under the practical AMI specified conditions. However, the transmission success rates decline in high traffic environments. Detailed analyses indicate the degradation of the performance is caused by the timeout problem which occurs when the destination terminal is in the wait duration of the data transmission, and so does not transmit an RIT data request frame. To overcome this problem, we propose the eF-RIT protocol that suppresses the frequency of timeout occurrence. The proposed eF-RIT protocol is also evaluated by simulation and experiment. The evaluation results indicate that the proposed eF-RIT protocol reduces the incident of timeout by up to 31%, and achieves transmission success rates as high as 90% when the data generation rate is 1.0×10-2s-1.

This paper summarizes Wi-SUN communication systems and their physical (PHY) layer and media access control (MAC) specifications. Firstly, the Wi-SUN communication systems are categorized into three. The key PHY and MAC standards, IEEE 802.15.4g and .4e, that configure the systems are explained, and fundamental transmission performances of the systems in the PHY layer and MAC layer are evaluated by computer simulations. Then, the Wi-SUN alliance and the Wi-SUN profiles that include IEEE 802.15.4g and .4e are explained. Finally, to understand the transmission performance of actual IEEE 802.15.4g Wi-SUN radio devices, PER performances under AWGN and multipath fading environments are measured by using IEEE 802.15.4g compliant and Wi-SUN alliance certified radio modules. This paper is an instruction paper for the beginners of the Wi-SUN based communications systems.

This paper develops the first prototype hardware for a TDD two-way multi-hop relay network with MIMO network coding. Since conventional wireless multi-hop relay networks have the drawback of low data rate, TDD two-way multi-hop relay networks have been studied as a solution to realize high data rate recently. In these networks, forward and backward streams are spatially multiplexed by using interference cancellation techniques such as MIMO beamforming or MIMO network coding. In this paper, a demonstration system for the TDD two-way multi-hop relay network with MIMO network coding (called 2-way relay network hereafter) is developed using the prototype hardware. In the demonstration system, each transmitter and receiver performs network coded broadcast and MIMO multiple access, respectively. By using the demonstration system, network throughput is measured in an indoor environment to prove the realization and effectiveness of the 2-way relay network. From the results of network throughput, it is found that the 2-way relay network can achieve high network throughput approaching theoretical upper bound even in low average end-to-end SNR area where network throughput of the direct link degrades severely. From these results, the realization and effectiveness of the 2-way relay network can be proved in the real indoor environment.

In this paper, we propose two schemes that improve the delay and the current consumption for efficient polling communications in multi-hop networks based on the receiver-initiated media access control (MAC) protocol. Polling communications can offer reliable data collection by avoiding communication collisions, but the larger delay and current consumption for the round-trip operation should be improved. The first proposal is an enhanced source routing scheme for downlink communications. In the proposed scheme, multiple candidates of relay terminals can be loaded in the routing information, so the route is not specified uniquely. The improvement of the delay and the current consumption is achieved by shortening the waiting time for communication timings based on the flexible routing. The second proposal is a round-trip delay reduction scheme which focuses on the bi-directionality of polling communications. The proposed scheme reduces the round-trip delay by offering frequent communication timings for uplink communications. Also, this paper proposes the joint application of the enhanced source routing scheme and the round-trip delay reduction scheme in polling communications. Computer simulations that suppose a multi-hop network based on the feathery receiver-initiated transmission (F-RIT) protocol in stable channel conditions are carried out. The results show the effectiveness of the proposed schemes in improving the delay and the current consumption. When the polling interval is 900s, the combination of the two proposed schemes improves the round-trip delay by up to 44.1% and the current consumption by up to 38.7% in average.

Setting relays can address the shadowing problem between a transmitter (Tx) and a receiver (Rx). Moreover, the Multiple-Input Multiple-Output (MIMO) technique has been introduced to improve wireless link capacity. The MIMO technique can be applied in relay network to enhance system performance. However, the efficiency of relaying schemes and relay placement have not been well investigated with experiment-based study. This paper provides a propagation measurement campaign of a MIMO two-hop relay network in 5 GHz band in an L-shaped corridor environment with various relay locations. Furthermore, this paper proposes a Relay Placement Estimation (RPE) scheme to identify the optimum relay location, i.e. the point at which the network performance is highest. Analysis results of channel capacity show that relaying technique is beneficial over direct transmission in strong shadowing environment while it is ineffective in non-shadowing environment. In addition, the optimum relay location estimated with the RPE scheme also agrees with the location where the network achieves the highest performance as identified by network capacity. Finally, the capacity analysis shows that two-way MIMO relay employing network coding has the best performance while cooperative relaying scheme is not effective due to shadowing effect weakening the signal strength of the direct link.

In-band full-duplex (IBFD) has been an attractive technology, which can theoretically double the spectral efficiency. However, when performing IBFD in the dynamic-duplex cellular (DDC) system, inter-user interference (IUI) deteriorates transmission performance in downlink (DL) communication and limits IBFD-applicable area and IBFD application ratio. In this paper, to expand the IBFD-applicable area and improve the IBFD application ratio, we propose an IUI reduction scheme using successive interference cancellation (SIC) for the DDC system. SIC can utilize the power difference and reduce the signal with the higher power. The effectiveness of the proposed scheme is evaluated by the computer simulation. The IUI reducing effect on the IBFD-inapplicable area is confirmed when the received power of the IUI is stronger than that of the desired signal at the user equipment for DL (DL-UE). The IBFD-inapplicable area within 95m from the DL-UE, where the IBFD does not work without the proposed scheme, can reduce by 43.6% from 52.8% to 9.2% by applying the proposed scheme. Moreover, the IBFD application ratio can improve by 24.6% from 69.5% to 94.1%.

This paper proposes out-of-band emission reduction schemes for IEEE 802.11af based Wireless Local Area Network (WLAN) systems operating in TV White Spaces (TVWS). IEEE 802.11af adopts Orthogonal Frequency Division Multiplexing (OFDM) to exploit the TVWS spectrum effectively. The combination of the OFDM and TVWS may be able to solve the problem of frequency depletion. However the TVWS transmitter must satisfy a strict transmission spectrum mask and reduce out-of-band emission to protect the primary users. The digital convolution filter is one way of reducing the out-of-band emission. Unfortunately, implementing a strict mask needs a large number of filter taps, which causes high implementation complexity. Time-domain windowing is another effective approach. This scheme reduces out-of-band emission with low complexity but at the price of shortening the effective guard interval. This paper proposes a mechanism that jointly uses these two schemes for out-of-band emission reduction. Moreover, the appropriate windowing duration design is proposed in terms of both the out-of-band emission suppression and throughput performance for all mandatory mode of IEEE 802.11af system. The proposed time-domain windowing design reduces the number of multiplier by 96.5%.

In this paper, we propose an IEEE 802.15.10-based layer 2 routing (L2R) method with a load balancing algorithm; the proposal considers fairness in terms of the cumulative number of sending packets at each terminal to resolve the packet concentration problem for the IEEE 802.15.4-based low-power consumption wireless smart utility network (Wi-SUN) systems. The proposal uses the accumulated sending times of each terminal as a weight in calculating each path quality metric (PQM) to decide multi-hopping routes with load balancing in the network. Computer simulation of the mesh network with 256 terminals shows that the proposed routing method can improve the maximum sending ratio (MSR), defined as the ratio of the maximum sending times to the average number of sending times in the network, by 56% with no degradation of the end-to-end communication success ratio (E2E-SR). The proposed algorithm is also experimentally evaluated by using actual Wi-SUN modules. The proposed routing method also improves the MSR by 84% with 70 terminals. Computer simulations and experiments prove the effectiveness of the proposed method in terms of load balancing.

Demand for wireless communication is increasing significantly, but the frequency resources available for wireless communication are quite limited. Currently, various countries are prompting the use of TV white spaces (TVWS). IEEE 802.11 Working Group (WG) has started a Task Group (TG), namely IEEE 802.11af, to develop an international standard for Wireless local Area Networks (WLANs) in TVWS. In order to increase maximum throughput, a channel aggregation mechanism is introduced in the draft standard. In Japan, ISDB-T based area-one-segment broadcasting system (Area-1seg) which is a digital TV broadcast service in limited areas has been permitted to offer actual TVWS services since April 2012. The operation of the IEEE 802.11af system shall not jeopardize the Area-1seg system due to the common operating frequency band. If the Area-1seg partially overlaps with the IEEE 802.11af in some frequency, the IEEE 802.11af cannot use the channel aggregation mechanism due to a lack of channels. As a result, the throughput of the IEEE 802.11af deteriorates. In this paper, the physical layer of IEEE 802.11af D4.0 is introduced briefly, and a partial subcarrier system for IEEE 802.11af is proposed to efficiently use the TVWS spectrum. The IEEE 802.11af co-exist with the Area-1seg by using null subcarriers. Computer simulation shows up to around 70% throughput gain is achieved with the proposed mechanism.

Non-linear behavioral models play a key role in designing digital pre-distorters (DPDs) for non-linear power amplifiers (NLPAs). In general, more complex behavioral models have better capability, but they should be converted into simpler versions to assist implementation. In this paper, a conversion from a complex fifth order inverse of a parallel Wiener (PRW) model to a simpler memory polynomial (MP) model is developed by using frequency domain expressions. In the developed conversion, parameters of the converted MP model are calculated from those of original fifth order inverse and frequency domain statistics of the transmit signal. Since the frequency domain statistics of the transmit signal can be precalculated, the developed conversion is deterministic, unlike the conventional conversion that identifies a converted model from lengthy input and output data. Computer simulations are conducted to confirm that conversion error is sufficiently small and the converted MP model offers equivalent pre-distortion to the original fifth order inverse.

In this letter, a neural network (NN) for peak power reduction of an orthogonal frequency-division multiplexing (OFDM) signal is improved in order to suppress its computational complexity. Numerical experiments show that the amount of IFFTs in the proposed NN can be reduced to half, and its computational time can be reduced by 21.5% compared with a conventional NN. In comparison with the SLM, the proposed NN is effective to achieve high PAPR reduction and it has an advantage over the SLM under the equal computational condition.

The Dynamic Spectrum Sharing (DSS) system, which uses the frequency band allocated to incumbent systems (i.e., primary users) has attracted attention to expand the available bandwidth of the fifth-generation mobile communication (5G) systems in the sub-6GHz band. In Japan, a DSS system in the 2.3GHz band, in which the ARIB STD-B57-based Field Pickup Unit (FPU) is assigned as an incumbent system, has been studied for the secondary use of 5G systems. In this case, the incumbent FPU is a mobile system, and thus, the DSS system needs to use not only a spectrum sharing database but also radio sensors to detect primary signals with high accuracy, protect the primary system from interference, and achieve more secure spectrum sharing. This paper proposes highly efficient sensing methods for detecting the ARIB STD-B57-based FPU signals in the 2.3GHz band. The proposed methods can be applied to two types of the FPU signal; those that apply the Continuous Pilot (CP) mode pilot and the Scattered Pilot (SP) mode pilot. Moreover, we apply a sample addition method and a symbol addition method for improving the detection performance. Even in the 3GPP EVA channel environment, the proposed method can, with a probability of more than 99%, detect the FPU signal with an SNR of -10dB. In addition, we propose a quantized reference signal for reducing the implementation complexity of the complex cross-correlation circuit. The proposed reference signal can reduce the number of quantization bits of the reference signal to 2 bits for in-phase and 3 bits for orthogonal components.

A variety of all-new systems such as a massive machine type communication (mMTC) system will be supported in 5G and beyond. Although each mMTC device occupies quite narrow bandwidth, the massive number of devices expected will generate a vast array of traffic and consume enormous spectrum resources. Therefore, it is necessary to proactively gather up and exploit fractional spectrum resources including guard bands that are secured but unused by the existing Long Term Evolution (LTE) systems. The guard band is originally secured as a margin for high out-of-band emission (OOBE) caused by the discontinuity between successive symbols in the cyclic prefix-based orthogonal frequency division multiplexing (CP-OFDM), and new-waveforms enabling high OOBE suppression have been widely researched to efficiently allocate narrowband communication to the frequency gap. Time-domain windowing is a well-known signal processing technique for reducing OOBE with low complexity and a universal time-domain windowed OFDM (UTW-OFDM) with a long transition duration exceeding the CP length has demonstrated its ability in WLAN-based systems. In this paper, we apply UTW-OFDM to the LTE downlink system and comprehensively evaluate its performance under the channel models defined by 3GPP. Specifically, we evaluate OOBE reduction and block error rate (BLER) by computer simulation and clarify how far OOBE can be reduced without degrading communication quality. Furthermore, we estimate the implementation complexity of the proposed UTW-OFDM, the conventional CP-OFDM, and the universal filtered-OFDM (UF-OFDM) by calculating the number of required multiplications. These evaluation and estimation results demonstrate that the proposed UTW-OFDM is a practical new-waveform applicable to the 5G and beyond.

In this paper, the world's first experimental evaluation of the Wi-SUN Japan Utility Telemetering Association (JUTA) profile-compliant feathery receiver-initiated transmission (JUTA F-RIT) protocol is conducted. Firstly, the transmission success rate in an interference environment is evaluated by theoretical analysis and computer simulations. The analysis is derived from the interference model focusing on the carrier sense. The analysis and simulation results agree as regards the transmission success rate of the JUTA F-RIT protocol. Secondly, we develop the dongle-type prototype that hosts the JUTA F-RIT protocol. Measurement results in a cochannel interference environment show that the transmission success rate at the lower MAC layer is around 94% when the number of terminals is 20. When the waiting time for the establishment of the communication link can be extended to exceed 10 s, the JUTA F-RIT protocol can achieve the transmission success rate of over 90% without the re-establishment of the communication link and re-transmission of data frames. Moreover, the experimental results are examined from two viewpoints of the performance of the frame transmissions and the timeout incident, and the feature of the JUTA F-RIT protocol are discussed.

The conventional universal filtered-DFT-spread-OFDM (UF-DFTs-OFDM) can drastically improve the out-of-band emission (OOBE) caused by the discontinuity between symbols in the conventional cyclic prefix-based DFTs-OFDM (CP-DFTs-OFDM). However, the UF-DFTs-OFDM degrades the communication quality in a long-delay multipath fading environment due to the frequency-domain ripple derived from the long transition time of the low pass filter (LPF) corresponding to the guard interval (GI). In this paper, we propose an enhanced UF-DFTs-OFDM (eUF-DFTs-OFDM) that achieves significantly low OOBE and high communication quality even in a long-delay multipath fading environment. The eUF-DFTs-OFDM applies an LPF with quite short length in combination with the zero padding (ZP) or the CP process. Then, the characteristics of the OOBE, peak-to-average power ratio (PAPR), and block error rate (BLER) are evaluated by computer simulation with the LTE uplink parameters. The result confirms that the eUF-DFTs-OFDM can improve the OOBE by 22.5dB at the channel-edge compared to the CP-DFTs-OFDM, and also improve the ES/N0 to achieve BLER =10-3 by about 2.5dB for QPSK and 16QAM compared to the UF-DFTs-OFDM. For 64QAM, the proposed eUF-DFTs-ODFDM can eliminate the error floor of the UF-DFTs-OFDM. These results indicate that the proposed eUF-DFTs-OFDM can significantly reduce the OOBE while maintaining the same level of communication quality as the CP-DFTs-OFDM even in long-delay multipath environment.