This paper proposes applying the Layered Orthogonal Frequency Division Multiple Access (OFDMA) radio access scheme and its radio access techniques to LTE (Long-Term Evolution)-Advanced to satisfy its system requirements, which are much stricter than those of the Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA) and UMTS Terrestrial Radio Access Network (UTRAN). Layered OFDMA comprises layered transmission bandwidth assignment (bandwidth is assigned to match the required data rate), a layered control signaling structure, and support for layered environments for both the downlink and uplink. Especially in the uplink, an adaptive multi-access scheme with hybrid single-carrier and multicarrier based radio access is applied. Layered OFDMA radio access will support all the functionalities specified in Release 8 LTE and later enhancements. Key radio access techniques such as fast inter-cell radio resource management that takes advantage of remote radio equipment (RRE) so as to realize inter-cell orthogonality, multi-antenna transmission with more antennas, and coverage enhancing techniques are used to achieve a high level of capacity and cell-edge spectrum efficiency.

This paper elucidates the most appropriate hybrid automatic-repeat-request (ARQ) scheme, i.e., which can achieve the highest throughput, for high-speed packet transmission in the W-CDMA forward link by comparing the throughput performance of three types of hybrid ARQ schemes: type-I hybrid ARQ with packet combining (PC), type-II hybrid ARQ, and basic type-I hybrid ARQ as a reference. Moreover, from the viewpoint of maximum throughput, the respective optimum roles of ARQ and channel coding in hybrid ARQ are also clarified, such as the optimum coding rate and the packet length related to the interleaving effect. The simulation results reveal that the type-II scheme exhibits the best throughput performance, and the required received signal energy per chip-to-background noise spectral density ratio (Ec/N0) at the throughput efficiency of 0.2/0.4/0.6 is improved by 0.7/0.3/0.1 dB and 3.9/1.8/0.5 dB, respectively, compared to the type-I scheme with and without PC in a 2-path Rayleigh fading channel with the average equal power at the maximum Doppler frequency of 5 Hz and the packet length of 4 slots (= 0.667 4 = 2.667 msec). However, the improvement of the type-II scheme compared to the type-I scheme with PC is small or the achievable throughput is almost identical in the high-received Ec/N0 region. On the other hand, the type-I scheme with PC is much less complex and thus preferable, while maintaining almost the same throughput performance or allowing very minor degradation compared to that with type-II. The results also elucidate that, while the optimum coding rate depends on the required throughput in the basic type-I and type-I with PC schemes, it is around between 3/4 and 8/9 in type-II, resulting in a higher throughput efficiency. In addition, for high-speed packet transmission employing a hybrid ARQ scheme, a shorter retransmission unit size is preferable such as 1 slot, and the fast transmit power control is effective only under conditions such as a low maximum Doppler frequency and a high transmit Ec/N0 region.

This paper compares the throughput performance employing hybrid automatic repeat request (ARQ) packet combining, i.e., Chase combining, and Incremental redundancy, considering the frequency diversity effect in the broadband forward-link channel for Orthogonal Frequency and Code Division Multiplexing (OFCDM) packet wireless access achieving a peak throughput above 100 Mbps. Simulation results show that the achievable throughput at the average received signal energy per symbol-to-background noise power spectrum density ratio (Es/N0) of 0 and 6 dB employing Incremental redundancy is increased by approximately 35 and 30% compared to that using Chase combining for QPSK and 16QAM data modulation schemes with the coding rate of R = 1/2, respectively, considering a large frequency diversity effect in a 12-path exponential decayed Rayleigh fading channel, since the reduced variations in the received signal level in a broadband channel bring about a larger coding gain in Incremental redundancy. We also show that when adaptive modulation and channel coding (AMC) is applied, Incremental redundancy is superior to Chase combining since the large coding gain is effective in achieving a large time diversity gain for a low number of retransmissions such as M = 1 or 2 for a maximum Doppler frequency up to fD = 400 Hz. It is demonstrated, nevertheless, that the total throughput when employing Incremental redundancy associated with a near optimum MCS set according to the channel conditions becomes almost identical to that using Chase combining when a large number of retransmissions, M, is allowed, such as M = 10, owing to time diversity along with frequency diversity.

This paper presents comprehensive comparisons of the achievable throughput between the 32-/64-ary amplitude and phase shift keying (APSK) and cross 32QAM/square 64QAM schemes based on mutual information (MI) considering the peak-to-average power ratio (PAPR) of the modulated signal. As a PAPR criterion, we use a cubic metric (CM) that directly corresponds to the transmission back-off of a power amplifier. In the analysis, we present the best ring ratio for the 32 or 64APSK scheme from the viewpoint of minimizing the required received signal-to-noise power ratio (SNR) considering the CM that achieves the peak throughput, i.e., maximum error-free transmission rate. We show that the required received SNR considering the CM at the peak throughput is minimized with the number of rings of M = 3 and 4 for 32-ary APSK and 64-asry APSK, respectively. Then, we show with the best ring ratios that the (4, 12, 16) 32APSK scheme with M = 3 achieves a lower required received SNR considering the CM compared to that for the cross 32QAM scheme. Similarly, we show that the (4, 12, 20, 28) 64APSK scheme with M = 4 achieves almost the same required received SNR considering the CM as that for the square 64QAM scheme.

Local (private) 5G system can provide a secure and flexible network using the cellular-based technologies at their facilities (e.g., factories, agricultural lands, and buildings). We constructed a small-scale demonstration system that exhibits the remote control of a patrol and work robot with arms using a local 5G system. The constructed robot comprises a robot operating system-based unmanned ground vehicle, two laser range finders, a webcam, an omnidirectional camera, and a six-axis robot arm. To fabricate a demonstration system with open-source software, we assessed the one-way delay of video streaming by changing different CPU, camera types, drivers, applications, and video resolutions. According to the assessment findings, it was demonstrated that it is possible to realize approximately 100ms delay under the limited resolution condition, and the allowable maximum absolute delay of 300ms can be attained even for full HD (1920 × 1080) resolution of this demonstration. Furthermore, local 5G was demonstrated to reduce delay variations to the same level as wired systems. It was also clarified that the increase in delay due to the application of local 5G is relatively small (5-25% in total delay) in this demonstration. Finally, we employed the small-scale demonstration system for the online and onsite campus tours for high school students.

Carrier aggregation (CA) is one of the most important techniques for LTE-Advanced because of its capability to support a wide transmission bandwidth of up to 100 MHz and heterogeneous networks effectively while achieving backward compatibility with the Release 8 LTE. In order to improve the performance of control information transmission in heterogeneous networks, cross-carrier scheduling is supported, i.e., control information on one component carrier (CC) can assign radio resources on another CC. To convey the control information efficiently, a search space is defined and used in Release 8 LTE. In cross-carrier scheduling, the optimum design for the search space for different CCs is a paramount issue. This paper presents two novel methods for search space design. In the first method using one hash function, a user equipment (UE)-specific offset is introduced among search spaces associated with different CCs. Due to the UE-specific offsets, search spaces of different UEs are staggered and the probability that the search space of one UE is totally overlapped by that of another UE can be greatly reduced. In the second method using multiple hash functions, a novel randomization scheme is proposed to generate independent hash functions for search spaces of different CCs. Because of the perfect randomization effect of the proposed method, search space overlapping of different UEs is reduced. Simulation results show that both the proposed methods effectively reduce the blocking probability of the control information compared to existing methods.

In Long-Term Evolution (LTE)-Advanced, heterogeneous networks where femtocells and picocells are overlaid onto macrocells are extensively discussed in addition to traditional well-planned macrocell deployment to improve further the system throughput. In heterogeneous network deployment, combined usage of inter-cell interference coordination (ICIC) and cell range expansion (CRE) is very effective in improving the system and cell-edge throughput. In this combined usage, the fraction of the sets of user equipment (UEs) connected to the picocells, which are controlled through CRE, and that connected to macrocells affect the gain from the ICIC. Therefore, this paper evaluates the throughput performance of different offset values for CRE and different amounts of protected resources for ICIC in picocell deployments in LTE-Advanced downlink. Simulation results (2–10 picocells and 30 UEs are located within 1 macrocell) assuming a full buffer traffic model show that when the CRE offset value is set between 8 to 20 dB, almost the same user throughput performance is obtained by allocating the appropriate resources to protect UEs that connect to the picocells. Furthermore, the appropriate resource ratio is derived based on the fraction of UEs connected to the picocells through CRE, the fraction of UEs connected to the macrocell, and the number of picocells under the simulation conditions.

This paper presents a comparison of the throughput performance employing hybrid automatic repeat request (HARQ) with packet combining, such as Type-I with packet combining (simply Chase combining hereafter) and Type-II (Incremental redundancy hereafter), using turbo coding in a multipath fading channel in high speed downlink packet access (HSDPA). We apply a multipath interference canceller (MPIC) to remove the influence of severe multipath interference. Link level simulation results show that the maximum throughput using Incremental redundancy with 64QAM is improved by approximately 5-8% compared to that using Chase combining, and that the required average received signal energy of 12 code channels per chip-to-background noise spectrum density (Ec/N0) at the throughput of 4 Mbps with Incremental redundancy is decreased by approximately 1.0 dB rather than that with Chase combining when the vehicular speed is higher than approximately 30 km/h. Furthermore, we elucidate based on the system level simulation that although no improvement is obtained in a slow mobility environment such as the average vehicular speed of 3 km/h, the achieved throughput of Incremental redundancy is increased by approximately 5-6% and 13% for the average vehicular speed of 30 km/h and 120 km/h, respectively, compared to that with Chase combining.

This paper presents experimental evaluations of the effect of time diversity obtained by hybrid automatic repeat request (HARQ) with soft combining in space and path diversity schemes on orthogonal frequency division multiplexing (OFDM)-based packet radio access in a downlink broadband multipath fading channel. The effect of HARQ is analyzed through laboratory experiments employing fading simulators and field experiments conducted in downtown Yokosuka near Tokyo. After confirming the validity of experimental results based on numerical analysis of the time diversity gain in HARQ, we show by the experimental results that, for a fixed modulation and channel coding scheme (MCS), time diversity obtained by HARQ is effective in reducing the required received signal-to-interference plus noise power ratio (SINR) according to an increase in the number of transmissions, K, up to 10, even when the diversity effects are obtained through two-branch antenna diversity reception and path diversity using a number of multipaths greater than 12 observed in a real fading channel. Meanwhile, in combined use with the adaptive modulation and channel coding (AMC) scheme associated with space and path diversity, we clarify that the gain obtained by time diversity is almost saturated at the maximum number of transmissions in HARQ, K ' = 4 in Chase combining and K ' = 2 in Incremental redundancy, since the improvement in the residual packet error rate (PER) obtained through time diversity becomes small owing to the low PER in the initial packet transmission arising from appropriately selecting the optimum MCS in AMC. However, the experimental results elucidate that the time diversity in HARQ with soft combining associated with antenna diversity reception is effective in improving the throughput even in a broadband multipath channel with sufficient path diversity.

This paper presents the average block error rate (BLER) performance of circular 32QAM and 64QAM schemes employing a frequency domain equalizer (FDE) for discrete Fourier transform (DFT)-precoded orthogonal frequency division multiplexing (OFDM) in multipath Rayleigh fading channels. The circular QAM scheme has an advantageous feature in that the fluctuation in the amplitude component is smaller than that for the cross or rectangular QAM scheme. Hence, focusing on the actual received signal-to-noise power ratio (SNR) taking into account a realistic peak-to-average power ratio (PAPR) measure called the cubic metric (CM), we compare the average BLER of the circular 32QAM and 64QAM schemes with those of cross 32QAM and rectangular 64QAM schemes, respectively. We investigate the theoretical throughput of various circular 32QAM and 64QAM schemes based on mutual information from the viewpoint of the minimum Euclidean distance. Link-level simulation results show that the circular 32QAM and 64QAM schemes with independent bit mapping for the phase and amplitude modulations achieves a lower required average received SNR considering the CM than that with the minimum Euclidean distance but with composite mapping of the phase and amplitude modulations. Through extensive link-level simulations, we show the potential benefit of the circular 32QAM and 64QAM schemes in terms of reducing the required average received SNR considering the CM that satisfies the target average BLER compared to the cross 32QAM or rectangular 64QAM scheme.