This paper examines a security enhancement technique from a passively secure hierarchical identity-based identification (HIBI) protocol to a concurrently secure one. Two types of security enhancement techniques for the identification protocols have been proposed: one based on the OR-proof technique and the other using a chameleon hash function. The former has been examined in detail, while the latter has not been formulated in the HIBI protocol, and its close evaluation of applicability, especially in identity-selecting settings, and reduction efficiency has not been made public. We describe a transformation using a chameleon hash function and compare it with the others based on the OR-proof technique in applicability and reduction efficiency.

This paper investigates the block error rate (BLER) performance of time and frequency domain compression for Faster-than-Nyquist (FTN) signaling in frequency-selective fading channels. In this paper, we use FTN mapping method in which FTN symbols are mapped onto orthogonal frequency division multiplexing (OFDM)/offset quadrature amplitude modulation (OQAM) symbol positions at a transmitter and a turbo soft interference canceller (SIC) used for an antenna-diversity receiver. Computer simulation results show that frequency domain compression decreases the required average received signal-to-noise power ratio satisfying the target average BLER compared to time domain compression when the root mean square (r.m.s.) delay spread is longer than approximately 1.5 μs. We also show, however, that the FTN signaling with time domain compression achieves a higher frequency efficiency compared to that with frequency domain compression when the r.m.s. delay spread is less than 1.5 μs.

This paper presents the link-level performance of downlink non-orthogonal multiple access (NOMA) with successive interference cancellation (SIC) receiver, considering the influence of error vector magnitude (EVM). In our evaluations, for the case of a 1-by-2 transmission and the number of NOMA multiplexed users is two, we clarify the performance of NOMA for cell-center user equipment (UE) with codeword level SIC (CWIC) receiver and the performance of the cell-edge UE, which does not apply SIC. Based on link-level performance evaluations, we show that the performance of CWIC receiver is almost the same as that of ideal SIC when the allocated transmit power ratio to cell-center UE is less than 0.35, the modulation and coding scheme (MCS) of cell-center UE is 16QAM (R = 0.51) or 64QAM (R = 0.47), and the MCS of cell-edge UE is QPSK (R = 0.51). Furthermore, we also show that, when EVM value is 4 % and the allocated power ratio to cell-center UE is between 0.2 and 0.37, the level of degradation due to the influence of EVM is below 0.6 dB, which is almost the same level of degradation as that of orthogonal frequency division multiple access (OFDMA) for the EVM value required by 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE). On the other hand, we show that the influence of EVM is marginal for cell-edge UE compared to cell-center UE. However, when the cell-center UE uses a higher order modulation such as 64QAM, we show that the required SNR of cell-edge UE increases due to the increase in inter-user interference. Based on these results, we clarify that it is important for the base station (BS) to take into account the target BLER and influence of EVM when selecting the MCS and allocated transmit power ratio of NOMA UEs.

Non-orthogonal multiple access (NOMA) has been attracting a lot of attention as a promising downlink multiple access scheme for LTE enhancements and 5G. This paper introduces an overview of the concept, performance evaluation gains and our experimental trials related to NOMA. The goal is to clarify the benefits of NOMA over orthogonal multiple access (OMA) such as OFDMA adopted by Long-Term Evolution (LTE), also its combination with MIMO is discussed. Using computer simulations, NOMA performance gains are assessed from both link-level and system-level perspectives. Also, our NOMA test-bed and the measurement results are explained. Our evaluation results and measurements show that NOMA provides higher gains compared to OFDMA. These gains are more than 30%.

This paper presents field experimental results on a vertical antenna element grouping for Smart Vertical (SV)-Multiple-Input Multiple-Output (MIMO) in the Long Term Evolution-Advanced downlink. Experimental results clarify that SV-MIMO achieves a higher fading correlation compared to a horizontally-arranged antenna configuration when the same antenna spacing is used. Then, when the combination of SV-MIMO and multi-user (MU)-MIMO is employed, we confirm that a gain is obtained by adaptively selecting the spacing among antenna element groups (group spacing) based on the different periods of the antenna grating lobes for each transmission mode. Finally, in measurement courses in urban and suburban areas, field experimental results show that the total throughput of greater than 1 Gbps is achieved for Rank 4 MU-MIMO by utilizing SV-MIMO with the group spacing of 3.1λ to 9.4λ.

This paper presents field experimental results on a base station (BS) antenna configuration associated with the fading correlation when using 4-by-2 multi-user (MU) multiple-input multiple-output (MIMO) in the Long Term Evolution (LTE)-Advanced downlink. In field experiments conducted in urban and suburban areas, we consider four antenna configurations, i.e., combinations of cross-/co-polarized antennas with an antenna array/space diversity antennas. The field experimental results show that the cross-polarized antenna configuration with low and high correlated antenna pairs is very effective in achieving throughput of greater than 800 Mbps when 4-by-2 Rank-4 MU-MIMO is applied in a suburban area under line-of-sight (LOS) conditions. In an urban area, where the majority of the measurement course is under non-LOS (NLOS) conditions, the experimental results show limited improvement in throughput for Rank-4 MU-MIMO. In this environment, we also show that Rank-2 MU-MIMO employing a space diversity antenna configuration achieves relatively high throughput irrespective of the angular difference between spatially multiplexed mobile stations.

This paper presents field experimental results on real-time 1-Gbps data transmission using 4-by-2 multi-user (MU) multiple-input multiple-output (MIMO) when a cross-polarized linear antenna array is employed as the base station (BS) transmitter antennas in the Long Term Evolution (LTE)-Advanced downlink. In the evaluations, we clarify the influence of the difference between directions of departure (DoDs) for two spatially multiplexed mobile stations (MSs) on the achievable throughput using experimental equipment, where eigenvalue decomposition (EVD)-based channel state information (CSI) feedback for each subband is implemented for MU-MIMO operation. Field experiments are conducted in urban and suburban areas where one MS travels at the average speed of 10 km/h and the other MS is static. Field experimental results show that the total throughput of greater than 1 Gbps can be achieved for Rank-4 MU-MIMO by utilizing a cross-polarized linear antenna array with low and high correlated antenna pairs when the difference between the DoDs for the spatially multiplexed MSs is within the range of approximately 40 to 70 and 50 to 55 degrees in suburban and urban areas, respectively. Furthermore, we show that the achievable throughput for Rank-2 MU-MIMO is relatively robust against the difference in the DoD and line-of-sight (LOS) or non-LOS (NLOS) conditions.

This paper presents laboratory experimental results on 4-by-2 multi-user (MU)-MIMO that achieves up to 1 Gbps throughput using carrier aggregation with a 100-MHz bandwidth in the LTE-Advanced downlink. The achievable throughput performance employing adaptive modulation and coding (AMC) with outer-loop threshold control based on acknowledgement (ACK) / negative ACK (NACK) feedback signaling in order to compensate for the fluctuation in the measured signal-to-interference plus noise ratio (SINR) value due to MU-MIMO multiplexing is evaluated using the implemented LTE-Advanced transceivers. Additionally, we evaluate the influence of the angle between spatially multiplexed users and the user combination in MU-MIMO operation with different received signal-to-noise ratio (SNR) conditions. Laboratory experimental results show that by performing AMC with outer-loop threshold control, the throughput of approximately 1 Gbps is achieved at the average received SNR of 30 dB. Furthermore, based on the experimental results, we confirm that angles narrower or wider than approximately 60 degrees between spatially multiplexed mobile stations (MSs) yield a lower ability to decrease the mutual interference using minimum mean square error (MMSE)-based precoding in 4-by-2 MU-MIMO. We also show that especially when the angle between spatially multiplexed MSs is narrower or wider than approximately 60 degrees, selecting the user pairs with a large difference in the average received SNR is effective in improving the total throughput.