High-altitude platform stations (HAPSs) using broad-band millimeter waves promise to enable the timely provisioning of the required high-speed large-capacity access in various locations including mountainous areas, air, and sea. Since no radio propagation measurements from the stratosphere to the ground have been conducted in the 38 GHz band, it is necessary to clarify the characteristics of radio propagation to realize the HAPS broadband system. In this paper, we report the world's first measurement of 38 GHz radio propagation from the lower stratosphere using a high-altitude aircraft, which was conducted in an environment closely similar to real HAPS operations. We present an evaluation of radio propagation characteristics under various elevation angles and weather conditions, as well as the influence of aircraft turning on radio propagation. Experimental results show that it is possible to apply Recommendations of the International Telecommunication Union Radiocommunication Sector (ITU- R) on attenuation values due to weather conditions for terrestrial radio links and satellite communication links to the stratospheric radio propagation environment under the influence of aircraft turning.

High-altitude platform stations (HAPSs) are promising to actualize extreme coverage extension from the stratosphere whereby mobile communications can be made available in various locations including mountainous areas, air, and sea. In particular, a fixed communications system for HAPS that uses the broadband millimeter-wave band will enable the provision of high-capacity communications infrastructure for many types of use cases such as high-capacity backhaul and industrial communications. However, the propagation delay is longer than that for ground systems, and processing delays caused by the HAPS stations and other devices are cumulative. Therefore, the system design must take these delays into account when implementing a network using HAPS. In this paper, to investigate the delay requirements in a fixed communications system for HAPS, we verify the transmission characteristics between a core network and a set of user equipment according to the insertion delay using a delay generator to emulate the delay caused by the HAPS and other system configurations. Up to now no transmission experiments have been reported that evaluate the impact of network latency on the communications quality in a fixed communications system for HAPS. Experimental results show that in the non-standalone 5th generation device environment used in this experiment, one-way delays of up to approximately 90 ms are acceptable, and that the observed communications performance is sufficient for the length of delay expected in a real-world environment.

5G New Radio (NR) takes multi-carrier waveform orthogonal frequency division multiplexing with cyclic prefix (CP-OFDM) with high spectral efficiency (SE) as the core waveform, and only supports single-carrier waveform discrete Fourier transform spreading OFDM (DFT-s-OFDM) with high power efficiency (PE) when uplink coverage is limited. 5G Evolution (5GE) and 6G have diversified scenarios, including high-frequency bands and integrated space-terrestrial systems, in which the non-linearity of power amplifiers (PA) restricts the system design. Therefore, high PE or low peak to average power ratio (PAPR) becomes one of the most significant key performance indicators (KPI) for 5GE and 6G waveform design, in addition to the high SE requirement. In this paper, we propose a unified non-orthogonal waveform (uNOW) based on DFT-s-OFDM enhancement with time-domain compression and expansion (TD-CE) as well as frequency-domain spectral shaping (FDSS) to improve PAPR and SE performance, simultaneously. Firstly, we describe the uNOW transmitter structure and two receiver structures, i.e., the linear minimum mean squared error (LMMSE) time-domain equalization (TDE) for time-domain compression and enhanced LMMSE frequency-domain equalization (FDE) for time-domain expansion. Then, the basic principle of uNOW is analyzed, i.e., how TD-CE and FDSS affect the time-domain pulse-shapes to reduce PAPR. Simulation results show that when only TD-CE or FDSS is considered, both PAPR gain and throughput gain are achieved compared with DFT-s-OFDM. When considering both TD-CE and FDSS, the PAPR and throughput gain achieved by uNOW can be significantly improved. Therefore, uNOW can be considered as a promising waveform candidate for 5GE and 6G.

Because communications in the future will be as commonplace as the air around us and as important a lifeline as power and water or even more so, the Fifth Generation (5G) Evolution and Sixth Generation (6G) mobile communications systems aim ultimately to expand coverage so that mobile services are available ubiquitously. Towards that goal, we present a new architecture for 5G Evolution and 6G that integrates non-terrestrial networks (NTNs) with terrestrial networks (TNs). The proposed cooperative NTN and TN architecture is promising as a means for expanding coverage in the future because it enables improved cost efficiency by sharing equipment and conservation of frequency resources through shared frequencies. In addition, by making full use of wireless technologies such as handover, carrier aggregation, and dual connectivity between NTNs and TNs, users can connect to 5G Evolution and 6G networks anywhere without being aware of the connection destination. In this paper, we propose a cooperative architecture that focuses on the link between NTNs and TNs, and a cooperative configuration with a particular focus on high-altitude platform stations (HAPSs). Furthermore, we present a HAPS performance evaluation using a 6G system-level simulator developed as a stepping stone for actualizing HAPS technology.

Non-linearity of power amplifiers (PA) is the restriction of waveform design for 5G Evolution (5GE) and 6G in high frequency bands with large bandwidth. The low peak to average power ratio (PAPR) single carrier waveform discrete fourier transform spreading orthogonal frequency division multiplexing (DFT-s-OFDM) can be used as a candidate waveform for 5GE and 6G. To satisfy the extremely high data rate requirement in 6G, how to keep the low PAPR of single carrier waveform and improve its spectral efficiency (SE) will be the challenge. In our previous study, a novel non-orthogonal waveform (NOW) design was proposed by combining DFT-s-OFDM with FTN to improve SE with low PAPR. However, due to the spectrum extension caused by FTN, large out of band emission (OOBE) and signal-to-noise ratio (SNR) loss were observed. In this paper, we propose an enhanced non-orthogonal waveform (eNOW) to improve the SE of DFT-s-OFDM by designing the frequency domain power allocation to efficiently suppress OOBE and reduce SNR loss. Simulation results demonstrate that the OOBE and SNR loss of eNOW can be significantly reduced than that of NOW by design the frequency domain power allocation. With eNOW scheme, OOBE, PAPR and throughput gain can be achieved, simultaneously.

High frequency bands with large bandwidth (e.g., millimeter-wave and terahertz frequencies) is promising for 5G Evolution and 6G, but the system design is restricted by the non-linearity of power amplifier (PA). Multi-carrier waveform of orthogonal frequency division multiplexing with cyclic prefix (CP-OFDM) may not be suitable for 5G Evolution and 6G due to its high peak to average power ratio (PAPR). Single carrier waveform represented by discrete fourier transform spreading OFDM (DFT-s-OFDM) with low PAPR could be a promising candidate waveform for 5G Evolution and 6G. Considering the extreme high data rate requirement of 5G Evolution and 6G, how to keep the low PAPR of DFT-s-OFDM and improve its spectral efficiency (SE) will be the challenge especially when high-order modulation is not applicable. In this paper, we propose a non-orthogonal waveform (NOW) to improve the SE of DFT-s-OFDM and derive the optimal time domain compression factor in terms of SNR based lossless compression. Furthermore, we investigate the impact of different compression factors to the system performance of throughput and PAPR. Simulation results demonstrate that the proposed scheme can achieve both throughput gain and PAPR gain over the traditional orthogonal waveforms DFT-s-OFDM and CP-OFDM, by flexibly adjusting the compression factor. When the compression factor is smaller than the optimal value, SNR loss to different extent may be observed.

This paper proposes a novel interleaver-linked receiver beamforming method for time division duplex (TDD)-interleave division multiple access (IDMA)-based random access. When the number of receiver antennas at the base station is large in a massive multiple-input multiple-output (MIMO) scenario, the channel estimation accuracy per receiver antenna at the base station receiver is degraded due to the limited received signal power per antenna from the user terminal. This results in degradation in the receiver beamforming (BF) or antenna diversity combining and user detection. In the proposed method, a unique receiver BF vector applied at the base station is linked to each of the M interleavers prepared by the system. The user terminal selects an appropriate pair comprising a receiver BF vector and an interleaver in advance based on the channel estimation results in the downlink assuming channel reciprocity in a TDD system. Therefore, the per-receiver antenna channel estimation for receiver BF is not necessary in the proposed method. Furthermore, we also propose an application of a transmitter channel equalization to the proposed method for effective channel shortening in order to increase the orthogonal preambles for channel estimation prepared for each interleaver. Computer simulations results show that the proposed method greatly improves the accuracy of user detection and channel estimation which results in reducing the error rate compared to the conventional method that performs channel estimation at each antenna in a massive MIMO environment.

In this paper, we propose a computational complexity-efficient algorithm called PCCNC for the adaptive peak-to-average power ratio (PAPR) reduction method using the null space in a multiple-input multiple-output (MIMO) channel for MIMO-orthogonal frequency division multiplexing (OFDM) signals. Based on our preliminary work, the proposed PCCNC in this paper newly introduces a parallel peak cancellation process at each iteration. By adding the multiple peak cancellation (PC) signals to the time-domain transmission signal vector simultaneously, the number of iterations in the iterative algorithm is reduced. The constraint so that the PC signal is transmitted only to the null space in the MIMO channel by beamforming (BF) makes interference from PC signal to the data streams not observed at the receiver side. Since the fast Fourier transform (FFT) and inverse FFT (IFFT) operations at each iteration are not required different from the conventional algorithm and thanks to the introduced parallel processing, the proposed PCCNC reduces the required number of iterations and total computational complexity compared to the conventional algorithm for achieving the same throughput-vs.-PAPR performance.

Due to the availability of wide bandwidth, high frequency band is promising for 5G evolution and 6G. With the increase of antenna ports and bandwidth, existing subband-level precoding consumes high feedback overhead and restricts the precoding granularity. However, channel sparsity can be observed in transformed angular-delay domain in mmWave systems with massive antennas. In this letter, to utilize the sparsity, we propose a transform domain precoding (TDP) to design precoder and feedback. Realistic factors including hybrid beamforming, frequency domain windowing and power allocation are analyzed and evaluated by link-level simulations. Results show that 60%~89% overhead reduction and 2.38%~21% spectrum efficiency (SE) enhancement can be achieved by TDP.

This paper presents outdoor field experimental results in the 28-GHz frequency band of a 5G radio access system where base stations (BSs) are installed on buildings to deploy a 5G trial area in the Tokyo Odaiba waterfront area. This is an early field trial assessment of key 5G features such as BS and mobile station (MS) beam tracking, being deployed in dense urban areas. In the trial area, a variety of key 5G technologies and conditions are evaluated such as BS and MS massive multiple-input multiple-output (MIMO) antennas, beamforming and tracking, use of the high 28-GHz frequency, the wide frequency bandwidth of 400 MHz, intra-baseband unit (BBU) hand over (HO), and a coverage area in a realistic urban deployment with four different trial courses. Experimental results show that throughput exceeding 1 Gbps is achieved in the experiment area, and approximately 200 Mbps is achieved at 500 m away from the BS. We confirm that beam tracking and intra-BBU HO operate effectively while compensating for high path loss in the 28-GHz band to achieve a coverage area of 500 m. On the other hand, line of sight (LoS) and Non-LoS conditions are critical to 5G performance in the 28-GHz band, and we find that 5G connections may drop behind trees, buildings, and/or under a footbridge. The trial results show that the downlink throughput exceeds 50 Mbps in 85%, 50%, 70%, and 33% of the four different trial courses, respectively.

We propose a decentralized probabilistic frequency-block activation control method for the cellular downlink. The aim of the proposed method is to increase the downlink system throughput within the system coverage by adaptively controlling the activation of each multiple frequency block at all base stations (BSs) to achieve inter-cell interference coordination (ICIC) and traffic load balancing effects. The proposed method does not rely on complicated inter-BS cooperation; it uses inter-BS cooperation only to share the temporal system throughput observed at the neighboring BSs. Based on the shared temporal system throughput information, each BS independently performs online activation control for the respective frequency blocks in a probabilistic manner, which autonomously achieves ICIC and load balancing effects among BSs. Computer simulation results, in which the mobility of the user terminals is taken into account, show the effectiveness of the proposed method.

This paper presents outdoor field experimental results in the 28-GHz frequency band of a 5G radio access system where base stations (BSs) and a core network are installed on buildings to deploy a 5G trial area in the Tokyo Odaiba waterfront area as a 5G trial site. This is the first report of a 5G trial in a realistic urban deployment in an approximate 1 square kilometer area using a single 5G network. In this trial area, a variety of key 5G technologies are evaluated such as the peak data rate and throughput performance, 5G coverage area, BS and mobile station (MS) massive multiple-input multiple-output antennas for beamforming and tracking, intra- and inter-baseband unit handover employing the high frequency of 28 GHz, and the wide frequency bandwidth of 400 MHz in a realistic urban deployment. Results show that coverage is provided for 88% of the assessed drive route and the downlink throughput of 650 Mbps is achieved for 80% of the route. As indicated when buildings block the radio signal, line of sight (LoS) or non-LoS (NLoS) conditions are critical for signal propagation in the 28-GHz frequency band. To improve coverage in NLoS areas, a portable BS using a wireless backhaul system is installed in the trial area. With the portable BS, the corresponding coverage area is increased from 50% to 83% along the assessed drive route resulting in improved downlink throughput from 600 Mbps to 660 Mbps, and 250 Mbps to 280 Mbps in the uplink.

This paper proposes an extension to a previously reported low latency hybrid automatic repeat request (HARQ) method that uses early retransmission prior to channel decoding to perform multistage judgment at early-retransmission decision. The previous method mitigates the increased transmission latency resulting mainly from the delay time required for channel decoding in HARQ by requesting early retransmission before the channel decoding process is completed based on the channel state information (CSI) obtained before channel decoding. However, the early-retransmission decision may include error that results in unnecessary retransmission and consequently throughput loss. To address the potential throughput loss due to the decision error in the early-retransmission request, we use multistage decision in which the number of bits conveyed by the early-retransmission packet is controlled dependent on the measured CSI before channel decoding. By setting the number of retransmitted coded bits to a low value when the observed channel state seems on the verge of performing early retransmission, we reduce the throughput loss when the early retransmission is not necessary since the initial packet is eventually channel decoded correctly. Simulation results show that the proposed extension further improves the achievable tradeoff between the transmission latency and throughput, which contributes to achieving ultra-reliable low latency communications (URLLC).

Higher bandwidth and spatial reuse through densification of wireless cells are necessary to meet the increase of wireless traffic demand in the next decade. Millimeter wave network can fulfill both of these criteria with the availability of abundant bandwidth and higher spatial reuse through directional beamforming. However, millimeter wave network suffers from coverage hole in urban environment due to blockage because of high path loss for millimeter wave signals. Wireless backhaul allows densification of mobile networks without incurring additional fiber deployment cost. Millimeter wave band based Integrated access and backhaul (IAB) is expected to provide a low cost coverage enhancement and capacity improvement solution. This paper focuses on the system performance of IAB node deployment in terms of coverage and user throughput by field experiment using millimeter wave band. The trial results prove that coverage ratio is significant improved with deploying IAB node. Meanwhile, dynamic resource allocation, including dynamic time division multiplexing (TDM) and dynamic TDM with flexible space division multiplexing (SDM) between access and backhaul link, brings obvious user throughput gain due to better resource utilization and providing more access transmission opportunities for User Equipment (UE) in backhaul slot.

We propose an online probabilistic activation control of base stations (BSs) considering both uplink and downlink system throughput. The proposed method is established by extending previous work on probabilistic BS activation control in which only the downlink system throughput is taken into account for maximization. In the proposed method, the total system throughput is defined to include both the uplink and downlink system throughput. The proposed method tries to find a set of activation states of all BSs in a decentralized manner to maximize the defined total system throughput. More specifically, each BS independently and iteratively updates the activation probability based on the time variation of the network-level total system throughput and the transition results of activated or deactivated states at that BS. We show the effectiveness of the proposed method quantitatively based on computer simulations.

This paper proposes a time-synchronized control-channel multiplexing scheme using cyclic-shifted Zadoff-Chu sequences for full duplex (FD) aiming at decreasing the latency due to feedback control signals. In the proposed scheme, a set of different cyclic-shift resources of a Zadoff-Chu sequence with the same root index are assigned to control signals in both the downlink and uplink that are multiplexed in time-synchronized subframes accompanied with a cyclic prefix and cyclic suffix. Because the cross-correlation of the different cyclic-shifted Zadoff-Chu sequences with the same root index is quite low, the self-interference (SI) or co-channel interference (CCI) that leaks from its own transmitter or that of another set of user equipment to a receiver is suppressed to a very low level after despreading in the frequency domain. As a result, the significantly reduced SI or CCI after despreading results in a decreased level of complexity for the SI or CCI canceller, i.e., particularly the digital interference canceller. The computed cross-correlation results show that the cross-correlations among different cyclic-shift indices become almost zero. Based on the computed cross-correlations of the cyclic-shifted Zadoff-Chu sequences, we discuss the receiver structures including SI rejection methods for a base station and UE. Because control signals are multiplexed in every subframe in the downlink and uplink, the proposed control-channel multiplexing is applicable to low-rate control signals that require low latency.

This paper proposes frequency diversity (FD) reception for narrowband (NB) primary synchronization signal (NPSS) and narrowband secondary synchronization signal (NSSS) in order to improve the physical-layer cell identity (PCID) detection probability for NB-Internet-of-Things (IoT) communications. In the proposed FD reception, a user equipment receives the NPSS and NSSS in a radio frame alternately in time domain by switching the received NPSS and NSSS each those are transmitted from different resource blocks in the same frequency band. Link-level simulation results show that the PCID detection probability using FD reception is improved by approximately 16% compared to that without FD reception using the FD separation of four resource blocks with single antenna transmission. These results suggest that the average time for computing the cost functions of the NPSS is decreased to approximately 1/3 that without FD reception for detecting the NPSS received timing. We also show that the PCID detection probabilities of 90% and 97% are achieved using FD reception with precoding vector switching (PVS) transmit diversity at the average received signal-to-noise power ratio of 0 dB for the case with the maximum frequency offset of 70 kHz and that without considering frequency offset, respectively.

The fifth-generation (5G) mobile communication system has attracted much attention to provide various kinds of services and applications for 2020 and later. To verify the feasibility of high presence public viewing service, the world's first maritime 5G experiment is conducted in Windsurfing World Cup 2018. In the experiment, 5G is used for 4K video transmission from a ship to public viewing area at land. This paper briefly reports that downlink and uplink maritime transmission performance of 5G employing 28 GHz band Massive MIMO (Multiple Input Multiple Output) and the success of the public viewing trial.

In full duplex (FD), which improves frequency efficiency and achieves flexible resource assignment between the uplink and downlink, the throughput cannot be improved to an ideal level due to self-interference (SI) from a transmitter, asymmetric traffic loads in the downlink and uplink, and other-cell interference. This paper proposes physical channel multiplexing using symbol repetition in every subframe for FD to improve the achievable throughput with an asymmetric traffic distribution. In the proposed physical channel multiplexing scheme, by employing symbol repetition in every subframe in the link with a low traffic load, i.e., the uplink typically, decreasing the power resource per symbol brings about an increase in throughput in the link with a high traffic load, i.e., the downlink, by decreasing the SI power level for FD. We describe the effect of latency and the implementation of an SI canceller focusing on a digital self-interference canceller (DSIC) for the proposed physical channel multiplexing scheme. We also show that the signal-to-interference plus noise power ratio (SINR) at the demodulator input is increased by employing the symbol repetition in every subframe, which leads to an increase in throughput in the link with a high traffic load for FD.

The commercialization of 5G is planned by multiple operators worldwide in the coming few years around 2020. 5G is expected to support new services and higher frequency bands. In particular, the use of higher frequency bands above 6 GHz for mobile communications is one new and important technical challenge tackled by 5G. However, in the initial deployments of 5G, higher frequency bands would only be used for limited areas, e.g., small cell deployments, or fixed wireless access. To further extend the benefits of higher frequency bands to wider coverage and usage, it is important to enable a wide use of higher frequency bands to a similar level as those of existing low frequency bands in terms of coverage, power consumption, etc. In this paper, we present our outdoor experimental trials of long range mobile communications using 39 GHz band. The trial results demonstrate the potential of higher frequency bands to support Gbps class data rates while still providing coverage and supporting mobility over a coverage area of above 1 km.

Non-orthogonal multiple access (NOMA) is a novel multi-user multiplexing scheme that improves spectral efficiency for LTE enhancements and 5G. By overlapping radio resources (e.g., time/frequency/code), but assigning different powers to the multiplexed users, NOMA is able to improve the system performance and fairness. To assess the performance of downlink NOMA under realistic conditions and confirm its feasibility with real hardware, we conducted experimental trials in outdoor environments using smartphone-sized NOMA chipset-embedded devices. This paper introduces our trial setup and trial results of NOMA combined with closed-loop 4×2 SU-MIMO.

The fifth generation mobile communications (5G) system will need to support ultra-reliable and low-latency communications (URLLC) to enable future mission-critical applications, e.g., self-driving cars and remote control. In this paper, we clarify coverage and mobility performance of URLLC by field experimental trials. To achieve URLLC requirements in 5G, we use a new frame structure, which adopts wider subcarrier spacing and acknowledgement/negative acknowledgement-less (ACK/NACK-less) retransmission to reduce the user-plane latency and improve the packet success probability, in this trial. We evaluate the URLLC coverage for several packet sizes using our prototype test-bed. The results show that URLLC requirement in 3GPP can be achieved in UL even when SNR is approximately -3.1 dB. Furthermore, we clarify that the requirement can be satisfied with 25 km/h mobility.

This paper presents outdoor experimental results with a 4 layer single-user (SU)-multiple-input multiple-output (MIMO) 5G cellular radio access system. Beam tracking with narrow beams are evaluated in the 15-GHz frequency band in order to investigate the effects of user mobility. In addition, distributed MIMO beamforming functionality is implemented to extend coverage using multiple transmission points (TPs) supporting 2 layers each. The experimental result in an outdoor open space environment shows that the peak throughput is 12.1 Gbps on a public road at an average speed of approximately 10 km/h. The result also shows that more than 8 Gbps is achieved at an average speed of approximately 40 km/h. Furthermore, it is observed that throughput is remarkably degraded when the difference in the received power between the best and second best transmission point is larger than 15 dB and only 2 layer spatial multiplexing is supported from one of the transmission points.

This paper proposes a low latency hybrid automatic repeat request (HARQ) method that uses the channel state information before channel decoding to address the increased transmission latency resulting mainly from the delay time required for the channel decoding in HARQ. We focus on applying the proposed method to ultra-reliable low latency communication. The proposed method reduces the transmission latency by requesting early retransmission before the channel decoding process is completed. We consider two metrics for deciding the early retransmission request: (1) mutual information (MI) calculated from the signal-to-noise ratio of the received packet and (2) the a priori log-likelihood ratio (LLR) of the coded bits obtained from the signal detection results of the received packet. Simulation results show that the proposed method successfully reduces the transmission latency at the cost of a very small loss in throughput. Between these two metrics, the MI-based method achieves a slightly better tradeoff between the throughput and transmission latency than the LLR-based method.

This paper presents indoor and outdoor experimental results on the achievable throughput for downlink 8-by-16 multi user (MU)-multiple-input multiple-output (MIMO) using 2 sets of user equipment (UE) and carrier aggregation with 8 component carriers in various measurement areas for 5G radio access. In the presence of four centralized antenna units, the throughput performance is evaluated using the implemented 5G testbed for MU-MIMO operation. The experimental results show that the peak system throughput of 18.6 Gbps and 25.9 Gbps are achieved in indoor and outdoor environments. Furthermore, we confirm that to avoid interference a vertical angle exceeding 18 deg. or a horizontal angle exceeding 10.7 deg. is required between UEs to achieve the throughput of 12 Gbps for a UE when employing MU-MIMO in an outdoor open space.

This paper presents indoor and outdoor experimental results on 4-by-8 single-user (SU)-multiple-input multiple-output (MIMO) multiplexing based on 730.5 MHz bandwidth transmission when applying carrier aggregation (CA) with 8 component carriers (CCs) in a 15 GHz frequency band in the downlink of 5G cellular radio access. Beam tracking with massive MIMO is implemented in a 5G testbed to support user mobility with a narrow beam. In addition, channel state information (CSI) acquisition functionality is implemented for the scheduler to select appropriate beams. Experimental results in an indoor multi-path rich environment show the gain up to 34 % with CSI acquisition compared to the case of without CSI acquisition in a line-of-sight (LoS) environment with high rank MIMO transmission. The results also show the gain up to 55 % with CSI acquisition compared to the case of without CSI acquisition in LoS conditions due to reflections by buildings.

This paper presents outdoor field experimental results that clarify 4-by-8 multiple-input multiple-output (MIMO) in the downlink throughput performance when applying distributed MIMO in the 28 GHz frequency band of a 5G cellular radio access system. A variety of transmission point (TP) deployments with narrow antenna beam forming is evaluated in order to investigate the downlink and uplink throughput performance and appropriate TP deployment for distributed MIMO. The experimental results show that the throughput is limited to approximately 7 Gbps in the downlink and 1 Gbps in the uplink in a parking area with localized MIMO. A distributed MIMO throughput gain is achieved with various TP deployments for both the downlink and uplink using two radio units. The outdoor parking area is an open space and multipaths are not anticipated, so a distinct advantage from distributed MIMO is expected. The distributed MIMO gain of 60% in the downlink and from 50 to 200% in the uplink is achieved at the cumulative distribution function of 80%. As a result of implementing distributed MIMO, throughput exceeding 10 Gbps in the downlink and 1.9 Gpbs in the uplink is achieved in the 28-GHz frequency band.

Massive multiple-input multiple-output (MIMO) has been considered as one of the key technologies in 5G communication, owing to its promising potential to increase the spectrum efficiency significantly. The capacity grows rapidly with the increasing number of antennas. However, in real-time environment, the more antennas are employed, the more computing resources are required, and this increase is even in a nonlinear progression. In this work, radio computing architecture (RCA) with multiple parallel general purpose processors (GPPs) and automatic distribution system (ADS) are utilized to overcome the strict real-time constraints and establish a highly flexible prototype platform for massive MIMO research. The feasibility and performance of the GPP-based prototype has been investigated through field trial. A collocated 64-RF-channel base station (BS) with each RF channel driving 3 antennas can simultaneously serve twelve 8-antenna user equipments (UEs). The maximum overall bandwidth is 200 MHz, and the maximum flow number is pre-defined as 24. In this field trial, a peak total user throughput of 11.29 Gbps and a cell spectrum efficiency of 79.82 bps/Hz are achieved. As far as we know, this is the world's highest throughput ever achieved in the sub 6 GHz band. Furthermore, apart from multi-user MIMO, single-user MIMO is also tested in this field trial.

This paper presents field experiments on the downlink throughput performance of a 5G centimeter wave radio access system employing higher rank MIMO in a shopping mall environment and a long corridor environment. The shopping mall has complex reflection paths within its non-line-of-sight areas. The long corridor environment exhibits line-of-sight propagation with many reflection paths. The results show that the maximum throughput of more than 4.8 Gbps in downlink is achieved with 400 MHz spectrum bandwidth in 20% of the course in the shopping mall environment. Moreover, the maximum Rank-8 transmission of more than 9.6 Gbps in downlink can be achieved in the long corridor environment.

This paper presents a field experimental trial on frequency-domain multiplexing of a mixture of multiple numerologies. The goal is to support diverse applications and services in the fifth generation mobile communications (5G) system. Frequency-domain multiplexing of mixed numerology has been discussed for 5G in order to flexibly support the variety of requirements introduced by future applications. However, frequency-domain multiplexing of mixed numerology causes inter sub-band interference. In this paper, we apply filtered-orthogonal frequency division multiplexing (f-OFDM), which is a new waveform, in order to reduce the inter sub-band interference. Through the field trial, we show that f-OFDM realizes mixed numerology while reducing the impact from inter sub-band interference compared to conventional cyclic prefix OFDM. The field trial results show that f-OFDM has no throughput degradation when using more than one guard subcarrier.

This paper presents indoor and outdoor field experimental results that clarify 4-by-8 multiple-input multiple-output (MIMO) downlink throughput performance applying distributed MIMO with a variety of transmission point (TP) deployments and narrow antenna beam tracking in the 15 GHz frequency band of a 5G cellular radio access system in order to investigate the appropriate TP deployment for distributed MIMO. Experimental results show that a throughput gain from distributed MIMO is achieved in various TP deployments in the lobby of an office building and an outdoor parking area using two radio units (RUs). In the lobby, a deployment where TP #1 covers the entire lobby and TP #2 covers areas around TP #1 that are non-line-of-sight exhibits a significant advantage over when distributed MIMO is not used yielding a throughput gain of 11 % over most of the area. In the outdoor parking area, a distinct advantage when using distributed MIMO is expected, and a gain in throughput of 124 % is achieved when TPs face the same direction and have a large separation between them over when distributed MIMO is not used. However, a large difference in the mobility reference signal received power (MRSRP) is also confirmed, especially in front of the TPs due to the large difference in the distance between the mobile station and the TPs. We find that if the second TP has a signal power below 14 dB of the first TP's signal, it does not contribute to the MIMO transmission. In order to compensate for the difference in MRSRP, four RUs are installed in the parking area, and the distributed MIMO gain of 77 % is achieved.

Radio frequency (RF) channel reciprocity calibration is one of the most important technologies in massive multiple-input multiple-output (MIMO) system. With the increasing of the antenna size, the calibration procedure becomes much more challenging. In this paper, wired- and wireless-calibration schemes have been proposed and investigated through field-trial test based on a real-time massive MIMO prototype with 64 independent RF channels. The prototype is capable of supporting 12 200-MHz user equipments (UEs) simultaneously. The field trial test results validate both schemes can significantly improve the overall system throughput. For single-user (SU) MIMO scenario, the throughput can be enhanced from 0.71 Gbps to 1.46 Gbps and 1.54 Gbps with wireless- and wired-calibration schemes, respectively. For multi-user (MU) MIMO scenario, the corresponding enhancement can be from 0.26 Gbps to 9.18 Gbps and 11.29 Gbps, respectively. In terms of calibration accuracy, the wired-calibration scheme has better performance, but the wireless one has lower system complexity and cost. To the best of our knowledge, this is the first field trial investigation of wireless-calibration scheme and comparison with wired calibration in a real-time high-throughput massive MIMO prototype.

The 5th generation of mobile communications system (5G) is nowadays expected to support very diverse applications, devices, and services such as enhanced mobile broadband (eMBB) and the Internet of things (IoTs). In order to meet the future requirements, new 5G candidate radio access technologies have been proposed and studied. For example, Massive multiple-input multiple-output (MIMO) is an attractive technology to further improve the spectrum efficiency and to boost system capacity. This paper presents a large scale field experimental trial of downlink time division duplex (TDD) Massive MIMO using the developed 5G test bed at the 4.5 GHz band. Specifically, the system performance of multi-user (MU) Massive MIMO with different numbers of sets of user equipment (UEs) and spatial layers is investigated, including the impact of different inter-UE separations and UE deployments, which have not been well investigated compared to the previous studies. The experimental results show that the throughput performance for a wide UE separation linearly increases as the number of layers and UEs increases, while the performance improvement is diminished when inter-UE separation narrows. In addition, the maximum total user throughput of 11.29 Gbps, which corresponds to a spectrum efficiency of 79.82 bps/Hz/cell, was achieved with 24 layers. The results indicate that TDD Massive MIMO using the developed 5G test bed greatly improves the spectrum efficiency for large scale MU-MIMO.

This paper proposes a fast cell search method using maximum likelihood detection (MLD) based frequency offset estimation for a small cell in Long Term Evolution (LTE) heterogeneous networks (HetNets). In the proposed cell search method, a set of user equipment (UE) estimates the primary synchronization signal (PSS) timing and frequency offset using different PSS correlation computation methods in a macrocell or a small cell according to the employed carrier frequency. For a macrocell, we use the conventional cross- correlation based detection. Meanwhile, for a small cell with a high carrier frequency, a UE first detects the maximum autocorrelation peak between the received sample signals that are five milliseconds apart. Then, the UE estimates the fractional frequency offset from the phase rotation between two consecutive PSSs. After compensating for the fractional frequency offset, the UE simultaneously detects the accurate frequency offset that provides the phase rotation of 2PIxG (G denotes an integer) over the multiplexed interval of two PSSs and the PSS sequence based on MLD. After selecting the best cell, the UE detects the best secondary synchronization signal (SSS) sequence by taking the SSS sequence correlation for the received signal. System-level simulation results show that the proposed cell search method achieves a fast initial cell search time within approximately 120 ms to satisfy the physical cell ID detection probability of 95% even for the carrier frequency of a small cell up to 12 GHz, assuming the free- running frequency error of the UE standard oscillator of 3 ppm.

This paper presents measurement results from different deployments with a 5G test-bed on a 15-GHz frequency band. The beam gain with a grid-of-beam solution applied to an 8x8 element antenna array is compared with a reference wide-beam power equivalent antenna. The beamforming gain in outdoor environment is found to be large, it is in the range of 10-13 dB in line-of-sight (LoS) and 7-12 dB in non-LoS. In a reflective and rich indoor environment, the gain is as expected lower but still substantial, 5-11 dB. The potential of a hybrid analog-digital solution is also assessed as an upper bound with perfect phase coherent combination of several beams. To reach an average beamforming gain of 14 dB it is sufficient with the combination of three beams in outdoor LoS, while eight beams are required in the indoor scenario.

Service diversity is expected in the upcoming fifth-generation (5G) cellular networks, which poses great challenges to the underlying waveforms to accommodate heterogeneous service requirements in a flexible way. By dividing the bandwidth into several subbands, each having a different numerology, this paper reports a field trial in time division duplex downlink conducted on a configurable test bed in a real-world environment for the performance evaluations of orthogonal frequency-division multiplexing (OFDM)-based 5G waveform candidates, i.e., cyclically prefixed OFDM (CP-OFDM), windowing OFDM (W-OFDM), and filtered OFDM (f-OFDM), in the presence of mixed numerologies. Field trial results confirm the feasibility of mixed numerologies and reveal the impact of several important system parameters, e.g., guard bandwidth, data bandwidth, signal-to-noise ratio (SNR), and transmit power. The results also suggest that f-OFDM outperforms CP-OFDM and W-OFDM in terms of both the spectrum efficiency and robustness in a high SNR regime, and the gain increases with a higher inter-numerology out-of-band interference. In some specific scenarios, ideal spectrum utilization can be realized by f-OFDM which completely removes the guard band.

Spectral efficiency is always a key factor to be improved and optimized along mobile communication networks evolving generation by generation. 5G enabling technologies must take spectral efficiency into consideration. In this paper, we show the performance of three key 5G technologies in sense of spectral efficiency improvement. Sparse code multiple access, polar codes, and filtered orthogonal frequency-division multiplexing are novel multiple access technology, channel coding scheme, and waveform, respectively. The combination of them is implemented in a 5G field trial testbed by NTT DOCOMO and Huawei for the first time. According to the field test results, we achieve over 100% spectral efficiency improvement comparison with baseline, where orthogonal frequency-division multiple access and turbo coding as LTE are used.

This paper presents indoor experimental results showing the achievement of 14.5 Gbps throughput performance based on 730.5 MHz bandwidth transmission when applying carrier aggregation (CA) with 8 component carriers (CCs) and 4-by-8 single-user multiple-input multiple-output (MIMO) multiplexing in the 15 GHz frequency band in the downlink of 5G cellular radio access. Beam tracking with massive MIMO is implemented in a 5G testbed to support user mobility with a narrow beam. Experimental results in an indoor multi-path rich environment show that the peak throughput is 14.5 Gbps in a line-of-sight (LoS) environment with high mobility-reference signal received power (MRSRP) and low antenna correlation. The results also show that 12.5 Gbps is achieved behind a wall in non-LOS conditions due to ceiling reflections.

Recently, NTT DOCOMO and Huawei conducted a large-scale experimental trial of key technologies for the 5th generation (5G) mobile systems. Downlink multi-user (MU) transmission with massive MIMO in the time-division duplex (TDD) mode is one of the technologies evaluated in this trial. With linear and non-linear downlink precoding schemes, we investigated the practical performance of MU massive MIMO systems under different numbers of users, user distributions, and different radio frequency channel calibration settings with up to 24 users deployed. When linear precoding is used, the cell spectrum efficiency reaches 39 bit/s/Hz, and it reaches 43 bit/s/Hz when non-linear precoding is used. In term of the cell throughput, up to 1.35 Gbps cell throughput was observed with a linear precoder and 100 MHz bandwidth; and 343 Mbps cell throughput was observed with a non-linear precoder and 20 MHz bandwidth. Based on these investigations, we verified the feasibility and performance of a TDD massive MIMO system for 5G mobile systems, and studied the impact of key factors on the system performance.

In the fifth generation mobile communications system (5G), it is expected to use millimeter wave (mmW) radio access with very wide frequency bandwidths of more than 1 GHz. To achieve good coverage and availability, high gain antennas or arrays are essential in order to compensate for the higher propagation loss experienced at mmW frequencies relative to current cellular bands. This paper presents the beamtracking performance and throughput performance of a 5G mmW Proof-of-Concept (PoC) system in field experiments conducted at up to 20 km/h vehicular speeds in outdoor line-of-sight (LOS) conditions. In addition, this paper recomposes the frame structure for low latency and evaluates latency performance in the vehicular experiments.

This paper proposes a fast initial cell search method based on two-step frequency offset estimation for a small cell in Long Term Evolution (LTE) heterogeneous networks using different frequency spectra. In the proposed cell search method, a set of user equipment (UE) first estimates the frequency offset of a received primary synchronization signal (PSS) from a macrocell and computes the frequency offset of a received PSS for a small cell in Step 1 assuming the same frequency error of a temperature compensated crystal oscillator (TCXO) of a UE. The UE detects the PSS received timing from the maximum PSS correlation after compensating for the frequency offset by using the estimated value in Step 1 for the small cell. In Step 2, the UE estimates the residual frequency offset by taking a partial correlation of the PSS from the small cell. The UE detects the best secondary synchronization signal (SSS) sequence by taking the SSS sequence correlation for the received signal after compensating for the frequency offset using the estimated value in Step 2. System- level simulation results show that the proposed cell search method achieves a fast initial cell search time within approximately 150 ms to satisfy the cell ID detection probability of 95% even for the carrier frequency of a small cell up to 6 and 11 GHz, assuming the free-running frequency error of the UE TCXO of 3 and 1 ppm, respectively.

We propose a trial concept that utilizes advanced multi-antenna solutions such as beamforming and spatial multiplexing with a massive number of antenna elements for use in a previously established trial system for the fifth generation (5G) mobile broadband communications system. Furthermore, we present experimental results showing that multi-user aggregated data rates exceeding 20 Gbps are possible in a real field environment.

5G is the next step in the evolution of mobile communication and a key component of the future networked society. With capabilities such as massive system capacity, higher data rates, very low latency and ultra-high reliability, 5G will provide significantly enhanced mobile-broadband experience but also support a wide range of new wireless applications and use cases. In this paper, a trial system for 5G mobile broadband operating at 15 GHz is outlined, together with initial experimental results showing that data rates of many Gbit/s are possible.

This paper presents experimental results on downlink transmission and beam tracking performance in an indoor shielded room environment using a Proof-of-Concept (PoC) system targeting 5G millimeter wave (mmW) radio access. Experiments in mmW targeting under mobility and beam tracking with narrow beams in reflective environment have not yet been conducted. The mmW transceiver is implemented with analog beamforming using a switched feeder array and a dielectric antenna. The experimental results show that a throughput of greater than 2 Gbps is achieved while employing beam tracking and a lens antenna. Furthermore, the performance in an anechoic camber was also evaluated. We conclude that the indoor shielded room has low reflections comparable to an anechoic chamber when using the mmW transceiver.

This paper presents outdoor field experimental results showing the achievement of 3-Gbps throughput performance based on 400-MHz bandwidth transmission when applying carrier aggregation with 4 component carriers and 4-by-4 single-user multiple-in multiple-out multiplexing in the 15-GHz frequency band in the downlink of 5G cellular radio access. A new radio interface with time division duplexing and radio access based on orthogonal frequency-division multiplexing is implemented in a 5G testbed to support ultra-high speed transmission with low latency. Experimental results in an outdoor open-space parking area show that the peak throughput is 2.8 Gbps in front of a base station (BS) antenna with a high reference signal received power (RSRP) although rank 2 is selected due to the high antenna correlation. The results also show that the average throughput of 2 Gbps is achieved 120 m from the BS antenna. In a courtyard enclosed by building walls, 3.6 Gbps is achieved in an outdoor-to-outdoor environment with a high RSRP and in an outdoor-to-indoor environment where the RSRP is lower due to the penetration loss of glass windows, but a multipath rich environment contributes to actualizing a low antenna correlation.

This paper focuses on the combination of coordinated multipoint (CoMP) transmission and Smart Vertical (SV)-Multiple-Input Multiple-Output (MIMO) base station (BS) antenna in the LTE-Advanced downlink to analyze the synergy effect on the combination, so that it presents experimental results on the combination. We investigate the gain of CoMP joint transmission (JT) and dynamic point selection (DPS) compared to non-CoMP transmission, and install a SV-MIMO antenna as BS antennas. Field experiments, which are conducted in a urban and suburban area in Japan, show that the achievable user throughput of CoMP DPS is from 20 % to 180 % greater than that for non-CoMP transmission, and no remarkable difference between CoMP JT and CoMP DPS within 5% throughput. With implementing SV-MIMO BS antenna for combination of CoMP DPS, up to 180 % throughput gain is achieved compared to using the conventional BS antenna. Finally comparing the throughput performance over different tilt angle, there is not remarkable difference for CoMP DPS transmission in both urban and suburban area.

5G is the next step in the evolution of mobile communication and a key component of the future networked society. With capabilities such as massive system capacity, higher data rates, very low latency and ultra-high reliability, 5G will provide significantly enhanced mobile-broadband experience but also support a wide range of new wireless applications and use cases. In this paper, a trial system for 5G mobile broadband operating at 15 GHz is outlined, together with initial experimental results showing that multi-Gbps data rates are possible.

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) is a promising multiple access scheme for further improving the spectrum efficiency compared to that for orthogonal multiple access (OMA) in the 5th Generation (5G) mobile communication systems. All of the existing evaluations for NOMA focus on the macrocell deployment since NOMA fully utilizes the power domain and the difference in channel gains, e.g., path loss, between users, which is typically sufficiently large in macrocells. Currently, small cells are becoming important and being studied for future Long-Term Evolution (LTE) enhancements in order to improve further the system performance. Thus, it is of great interest to study the performance of NOMA for small cell deployment under various environments. This paper investigates the system level performance of NOMA in small cells considering practical assumptions such as the single user multiple-input multiple-output (SU-MIMO) technique, adaptive modulation and coding (AMC), feedback channel quality indicator (CQI). Some of the key NOMA specific functionalities, including multi-user paring and transmit power allocation are also taken into account in the evaluation. Based on computer simulations, we show that for both macrocell and small cell deployments, NOMA can still provide a larger throughput performance gain compared to that for OMA.

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%.

A distributed antenna system, where antennas at a base station are spatially distributed over the cell, can improve throughput at the cell edge compared to a centralized antenna system. However, the peak capacity degrades when a remote antenna unit has a few antenna elements due to rank deficiency. In general, the number of antennas at the base station is limited by the number of pilot sequences. Thus, it is difficult to increase the number of antennas. In this paper, we use antenna splitting to increase the number of antennas without increasing the number of pilot sequences and evaluate the impact of antenna splitting on the sum capacity in a multiuser MIMO system. From computer simulations, it is shown that we can obtain higher sum capacity by increasing the number of antennas even though the number of pilot sequences is limited.

This paper extends our previously proposed non-orthogonal multiple access (NOMA) scheme to the base station (BS) cooperative multiple-input multiple-output (MIMO) cellular downlink for future radio access. The proposed NOMA scheme employs intra-beam superposition coding of a multiuser signal at the transmitter and the spatial filtering of inter-beam interference followed by the intra-beam successive interference canceller (SIC) at the user terminal receiver. The intra-beam SIC cancels out the inter-user interference within a beam. This configuration achieves reduced overhead for the downlink reference signaling for channel estimation at the user terminal in the case of non-orthogonal user multiplexing and also achieves the applicability of the SIC receiver in MIMO downlink. The transmitter beamforming (precoding) matrix is controlled based on open loop-type random beamforming using a block-diagonalized beamforming matrix, which is very efficient in terms of the amount of feedback information from the user terminal. Simulation results show that the proposed NOMA scheme with block-diagonalized random beamforming in BS cooperative multiuser MIMO and the intra-beam SIC achieves better system-level throughput compared to orthogonal multiple access (OMA), which is assumed in LTE-Advanced. We also show that BS cooperative operation along with the proposed NOMA in particular achieves a high cell-edge user throughput gain which implies better user fairness and universal connectivity.

This paper proposes an enhanced interference measurement method that provides accurate channel quality indicators (CQIs) to improve the system performance in coordinated multi-point (CoMP) transmission and reception. In CoMP operations, user equipments (UEs) need to report different CQIs based on different interference hypotheses. Even though a variety of interference measurement schemes are proposed, they always suffer higher complexity, inaccuracy or restriction in terms of the number of available interference measurement resource (IMR) configurations. In the proposed method, phase rotations are introduced for channel state information reference signals (CSI-RSs) before mapping to the resource grid. Both theoretical analysis and simulation results show that the proposed method improves the accuracies of both signal estimation and interference measurement, and consequently yields accurate CQIs. Moreover, it can provide a large number of IMR configurations.

As a promising downlink multiple access scheme for further LTE enhancement and future radio access (FRA), this paper investigates the system-level performance of non-orthogonal multiple access (NOMA) with a successive interference canceller (SIC) on the receiver side. The goal is to clarify the potential gains of NOMA over orthogonal multiple access (OMA) such as OFDMA, taking into account key link adaptation functionalities of the LTE radio interface such as adaptive modulation and coding (AMC), hybrid automatic repeat request (HARQ), time/frequency-domain scheduling, and outer loop link adaptation (OLLA), in addition to NOMA specific functionalities such as dynamic multi-user power allocation. Based on computer simulations, we show under multiple configurations that the system-level performance achieved by NOMA is superior to that for OMA.

Multiple-input multiple-output (MIMO) systems are well known as a method to improve the throughput performance. Recently, a concept of massive (or very large) MIMO using an antenna array with an order of 100 elements has been proposed. In a demand for low-complexity detection method, belief-propagation based algorithm, which is implementable in the order of the second power of the number of elements, has been developed. In the paper, the extrinsic information transfer (EXIT) analysis is applied to clarify the validity of iterative processing capability and evaluate the convergence performance. The results show that the EXIT chart expresses the BER convergence behavior well when the number of antenna elements is 100.

A very large MIMO system has a potential to achieve extremely-high system throughput. In general, however, algorithms detecting spatially-multiplexed signals require the complexity proportional to the cubed number of antenna elements in the least case. Thus, the implementation of an antenna array with an order of 100 elements becomes very difficult. In this paper, we focus on the algorithm which is based on belief propagation and implementable with the second-order calculations. The simulation results show that the algorithm provides very good BER performance in MIMO spatial multiplexing when the number of antenna elements is 100 and reasonably low complexity in comparison to the MMSE spatial filtering.

We propose an enhancement to the power allocation among multiple beams in our previously reported non-orthogonal access with random beamforming and intra-beam successive interference canceller (SIC) for cellular multiple-input multiple-output (MIMO) downlink. By equally allocating transmission power among multiple beams, the average user throughput within a cell can be enhanced due to the effective use of spatial multiplexing. The throughput of users at the cell edge may be improved by allocating non-equal transmission power among beams since the inter-beam interference is decreased and the received signal power is increased from the viewpoint of the main beam to which most of the transmission power is allocated. Aiming at further enhancement of the system efficiency and cell-edge user experience in our previous non-orthogonal access scheme, we propose coordinated frequency block-dependent inter-beam power allocation and inter-frequency block power allocation based on fractional frequency reuse (FFR) for inter-cell interference coordination. Based on simulation results, we show that the proposed power allocation method effectively enhances the tradeoff between the average and cell-edge user throughput.

We investigate non-orthogonal access with a successive interference canceller (SIC) in the cellular multiple-input multiple-output (MIMO) downlink for systems beyond LTE-Advanced. Taking into account the overhead for the downlink reference signaling for channel estimation at the user terminal in the case of non-orthogonal multiuser multiplexing and the applicability of the SIC receiver in the MIMO downlink, we propose intra-beam superposition coding of a multiuser signal at the transmitter and the spatial filtering of inter-beam interference followed by the intra-beam SIC at the user terminal receiver. The intra-beam SIC cancels out the inter-user interference within a beam. Furthermore, the transmitter beamforming (precoding) matrix is controlled based on open loop-type random beamforming, which is very efficient in terms of the amount of feedback information from the user terminal. Simulation results show that the proposed non-orthogonal access scheme with random beamforming and the intra-beam SIC simultaneously achieves better sum and cell-edge user throughput compared to orthogonal access, which is assumed in LTE-Advanced.

Coordinated multi-point (CoMP) transmission and reception is considered to be a promising technology to improve the cell-edge user throughput by mitigating the inter-cell interference, and it is expected to be specified in long-term evolution (LTE) Release 11 in 3GPP. For CoMP, the channel state information (CSI) feedback mechanism is a key factor in achieving a better throughput performance gain. This paper proposes two interference measurement schemes for CoMP in the LTE-Advanced downlink. In the proposed schemes, the existing CSI reference signal, which is used for CSI measurement, is fully utilized considering the impact to legacy user equipment, and a sufficient number of configurations for interference measurement resources are established to facilitate operator cell-planning efforts. Based on multi-cell link level and system-level simulations, we also confirm that the proposed schemes achieve an accurate interference measurement for a single transmission point and CoMP operation.

This paper presents a non-orthogonal multiple access (NOMA) concept for cellular future radio access (FRA) towards the 2020s information society. Different from the current LTE radio access scheme (until Release 11), NOMA superposes multiple users in the power domain although its basic signal waveform could be based on the orthogonal frequency division multiple access (OFDMA) or the discrete Fourier transform (DFT)-spread OFDM the same as LTE baseline. In our concept, NOMA adopts a successive interference cancellation (SIC) receiver as the baseline receiver scheme for robust multiple access, considering the expected evolution of device processing capabilities in the future. Based on system-level evaluations, we show that the downlink NOMA with SIC improves both the capacity and cell-edge user throughput performance irrespective of the availability of the frequency-selective channel quality indicator (CQI) on the base station side. Furthermore, we discuss possible extensions of NOMA by jointly applying multi-antenna/site technologies with a proposed NOMA/MIMO scheme using SIC and an interference rejection combining (IRC) receiver to achieve further capacity gains, e.g., a three-fold gain in the spectrum efficiency representing a challenging target for FRA.

This paper presents indoor experimental results on the achievable throughput for 4-by-2 multi-user (MU)-MIMO using 2 mobile stations (MSs) and carrier aggregation with 5 component carriers (90-MHz bandwidth) considering various transmitter antenna arrangements in the LTE-Advanced downlink. Under two centralized and two distributed antenna arrangement (CAAs and DAAs) conditions, the throughput performance is evaluated using the implemented LTE-Advanced transceiver, where extended channel state information (CSI) feedback based on eigenvalue decomposition (EVD) is implemented for MU-MIMO operation. The experimental results show that the peak throughput of greater than 1 Gbps is achieved for the CAAs in an indoor environment. The results also showed that although the MS moving speed strongly influences the throughput for Rank-4 MU-MIMO, MU-MIMO is robust against the antenna separation, i.e., fading correlation. Furthermore, we confirm that, in the DAAs, although the peak throughput of 1 Gbps is not observed, the throughput of approximately 700 to 950 Mbps is achieved.

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.

This paper presents experimental results to clarify the throughput performance and effective location probability for closed-loop single-user (SU)-MIMO transmission considering the effect of antenna configurations in the LTE-Advanced uplink. The achievable throughput performance with adaptive modulation and coding (AMC) and hybrid automatic repeat request (HARQ) is evaluated using the implemented LTE-Advanced transceivers, where the total transmission power and bandwidth per component carrier of a mobile station (MS) are set to 23 dBm and 17.28 MHz, respectively. The experimental results show that when 2-by-2 Rank-2 SU-MIMO, i.e., spatial multiplexing, is applied, a cross-polarized antenna configuration exhibits better throughput performance compared to that using co-polarized antennas and the location probability for achieving throughput greater than 200 Mbps is clearly increased. Furthermore, we confirm that the throughput performance using cross-polarized antennas is very robust against the variation in MS antenna angles irrespective of the rank values for SU-MIMO transmission. The experimental results also show that 2-by-2 Rank-2 SU-MIMO using the cross- polarized antennas improves the throughput performance compared to 1-by-2 SIMO at the location probability of greater than 60% even when the MS antenna gain imbalance level of 12 dB is considered.

This paper presents laboratory experimental results on the throughput performance of asymmetric carrier aggregation between the uplink and downlink using an LTE-Advanced testbed. The implemented base station (BS) and mobile station (MS) transceivers have transmission bandwidth capability of up to 100 MHz (5 component carriers (CCs)) and 40 MHz (2 CCs) in the downlink and uplink, respectively. The testbed also features CC-specific adaptive modulation and channel coding (AMC) and hybrid automatic repeat request (HARQ) functionalities based on the actually transmitted control signaling. The experimental results show that, in the uplink, CC-based AMC using up to 64QAM high-order modulation is effective in increasing the user throughput in multipath fading channels and achieves a throughput greater than 100 Mbps using carrier aggregation with 2 CCs and 1-by-2 SIMO. The results also show that when the uplink control information (UCI) corresponding to 5 downlink CCs is multiplexed onto the uplink shared channel (PUSCH), the required block error rate (BLER) of the UCI below 10-2 is almost satisfied by appropriately setting the offset value, , for adjusting the channel coding rate of UCI although AMC with high-order modulation is applied to the UCI as well. Furthermore, we show that when carrier aggregation with 5 CCs and 2-by-2 MIMO multiplexing are applied in the downlink, high throughput greater than 500 Mbps (thus, half of the 1 Gbps that can be achieved using 4-by-4 MIMO multiplexing) is achieved at the average received signal-to-noise power ratio (SNR) of approximately 25 dB when CC-specific AMC considering UCI error is applied.

This paper presents the laboratory experimental results employing LTE-Advanced testbed for the evaluation of the throughput performance of closed-loop single-user MIMO transmission at the uplink single carrier (SC)-FDMA radio access in LTE-Advanced. The throughput evaluation includes the impact of estimation accuracy of MIMO channel responses which are derived from the sounding reference signal (SRS) and used for the precoding vector (PV) selection and adaptive modulation and coding (AMC) at the base station. The experimental results elucidate that the maximum throughput of 200 Mbps is achieved in multipath fading environments by using 2-by-2 spatial multiplexing and carrier aggregation with 2 component carriers. The results also clarifies that the estimation accuracy of MIMO channel responses using the SRS has a greater influence on modulation and coding scheme (MCS) selection for AMC than PV selection due to the fact that the throughput performance employing AMC is clearly degraded by approximately 20% while the block error rate for Rank-1 closed-loop transmit diversity is not degraded very much when the transmission power ratio of SRS to data channel is reduced from 0 dB to -10 dB.

CoMP JP (Coordinated Multi-Point Joint Processing) is regarded as a promising technique to improve both cell edge user throughput and cell average user throughput in LTE-A downlink. CoMP JP can be categorized as CoMP JT (Joint Transmission) and COMP DCS (Dynamic Cell Selection). Compared with CoMP JT schemes, CoMP DCS provides a good trade-off between the transmission algorithm complexity, backhaul overhead and system performance. Conventional DCS scheme can benefit cell edge users by instantaneous selecting the best severed eNB for cell edge users based on limited signaling overhead in uplink radio interface. DCS with muting scheme further apply muting to the strongest neighbor cell for decreasing interference to cell edge users. However the system spectrum efficiency may be degraded, since frequency reuse one is not maintained and radio resource (resource block and power) may not be fully used. An enhanced DCS with muting method is proposed here to further improve the frequency and power efficiency, by using adaptive muting mode selection based on capacity calculation and flexible power allocation based on muting mode selection status. Performance evaluation shows the proposed algorithm can provide about 5.5% cell average throughput gain and about 10% cell edge throughput gain respectively compared with conventional DCS schemes.

In the LTE-Advanced downlink, to satisfy high-level performance requirements, advanced multi-antenna transmission techniques such as higher-order single-user (SU)-MIMO, multi-user (MU)-MIMO, and coordinated multi-point transmission/reception (CoMP) are key. At the 3GPP RAN WG1 meeting, the demodulation reference signal (DM-RS) was defined to support channel estimation and data demodulation for up to eight transmission layers. A hybrid code division multiplexing (CDM) and frequency division multiplexing (FDM) scheme was adopted as a DM-RS multiplexing scheme. The time-domain orthogonal cover code (OCC) is used for CDM since time domain orthogonality among OCCs is relatively robust against channel variation. However, in a medium-to-high mobility environment, orthogonality distortion occurs among OCCs, which results in performance degradation. In this paper, we propose a two-dimensional (2D) OCC that achieves two-dimensional orthogonality in the time and frequency domains to improve the performance of CDM-based DM-RSs while reducing the peak transmit power of each OFDM symbol where CDM-based DM-RS are mapped. Simulation results show that the 2D OCC is effective in improving the block error rate performance especially in a medium-to-high mobility environment. Furthermore, it is shown that the proposed 2D OCC effectively reduces the peak transmit power compared to the time-domain OCC.

This paper proposes the optimum radio link connection (RLC) using remote radio equipment (RRE) in a heterogeneous network in which various types of cell configurations exist with different cell sizes and downlink transmission power levels for LTE (Long-Term Evolution)-Advanced. The instantaneous received signal-to-interference plus noise power ratio (SINR) and the user throughput performance employing the proposed RLC methods are investigated using system-level simulations. From the simulation results, we show that the proposed independent RLC method between the downlink and uplink and the proposed multipoint RLC method based on coordinated multipoint transmission/reception achieve a higher user throughput both in the downlink and uplink compared to the conventional common RLC method. Therefore, the proposed independent and multipoint RLC methods are very promising candidates to improve the user throughput particularly near the cell edge in a heterogeneous network for LTE-Advanced.

This paper presents the effects of applying channel-dependent dynamic scheduling and transport block (TB) assignment that take advantage of a wider transmission bandwidth than that for a component carrier (CC) in OFDMA radio access for the LTE-Advanced downlink At the 3GPP RAN WG1 meeting, independent resource block (RB) assignment of one TB within one CC was adopted. However, gains in dynamic scheduling and TB assignment over a transmission bandwidth wider than that for a CC have not yet been sufficiently investigated, and these are crucial in obtaining target insight which is to be achieved by alternative techniques according to the adopted CC based TB assignment. Hence, we investigate the cell throughput and cell-edge user throughput gains for the three types of channel-dependent dynamic scheduling and TB assignment: TB assignment and dynamic scheduling within one CC, TB assignment within one CC and dynamic scheduling over multiple CCs, and TB assignment and dynamic scheduling over multiple CCs. Then, based on system-level simulation results, we present the comprehensive insights assuming the current working assumption for LTE-Advanced.

This paper investigates the optimum radio parameters, i.e., numerology, in layered orthogonal frequency division multiple access (OFDMA) for long-term evolution (LTE)- Advanced. Similar to the layered OFDMA concept, it was agreed at the 3GPP RAN WG1 meeting that the entire transmission bandwidth in LTE-advanced should comprise multiple frequency blocks called component carriers to achieve a wider system bandwidth than that for the current LTE (Rel-8 LTE). We investigate the optimum radio parameters in the frequency domain including the need for an inter-component carrier guard band (GB). In the simulation evaluations, we set the parameters for the receiver filter assuming the worst case that satisfies the minimum requirement specified in Rel-8 LTE. Simulation results show that the loss in the average received signal energy per symbol-to-noise power spectrum density ratio (Es/No) satisfying the required block error rate compared to the case without an inter-component carrier GB is negligible irrespective of the modulation scheme and coding rate. As a result, we conclude that the inter-component carrier GB is unnecessary and can be minimized to 19 subcarriers in the downlink while retaining the same number of subcarriers within a component carrier as that for Rel-8 LTE.

Tins paper presents the most appropriate transmit diversity scheme for the synchronization channel (SCH) employing the latest radio interface for the SCH structure and sequences based on system-level simulations in the evolved UTRA downlink. The transmit diversity candidates assumed in the paper are preceding vector switching (PVS), time switched transmit diversity (TSTD), cyclic delay diversity (CDD), and frequency switched transmit diversity (FSTD) based on the features of the SCH. Simulation results show that transmit diversity is effective in increasing detection probabilities of SCH timing detection in the first step and the cell ID group-specific SCH sequence in the second step of the cell search process. Moreover, we clarify that PVS is the best transmit diversity scheme for the SCH based on the reduction in the cell search time. We show that PVS achieves fast cell search in less than approximately 20 msec at the location probability of 90% regardless of the inter-site distance up to 10 km.

This paper proposes layered orthogonal frequency division multiple access (OFDMA) radio access for LTE (long-term evolution)-advanced to achieve higher-level system requirements than those in Release 8 LTE called Evolved UMTS terrestrial radio access (UTRA) and UMTS terrestrial radio access network (UTRAN). Layered OFDMA comprises layered transmission bandwidth assignment according to the required data rate, a layered control signaling structure, and support for layered environments in which an adaptive multi-access scheme with hybrid single-carrier and multicarrier based radio access is applied. layered OFDMA radio access will support all functionalities provided in Release 8 LTE and its enhancement. Key radio access techniques such as fast inter-cell radio resource management that take advantage of remote radio equipment (RRE) aiming at inter-cell orthogonality, multi-antenna transmissions with more antennas, and coverage enhancing techniques are used to achieve a high level of capacity and cell-edge spectrum efficiency.

This paper presents the optimum channel coding and multiplexing schemes for Layer 1 (Ll)/Layer 2 (L2) control signals for OFDM based radio access in the Evolved UTRA downlink. Simulation results show that separate channel coding of downlink-related L1/L2 control signals is superior to joint coding among simultaneous accessing user equipments (UEs), from the viewpoint of the required total symbol energy of the L1/L2 control signals. The results also show that time division multiplexing (TDM) based multiplexing associated with transmission time interval (TTI)-by-TTI frame format control employing a control channel format indicator (CCFI) achieves almost the same cell throughput as that for frequency division multiplexing (FDM). Therefore, considering the advantages of TDM such as the possibility of a power saving effect through micro-sleep operation and a short control loop delays for scheduling, adaptive modulation and coding, and hybrid ARQ, we conclude that TDM based multiplexing of L1/L2 control signals with a shared data channel is superior to using FDM based multiplexing.

Single-Carrier (SC)-FDMA based radio access in the evolved UTRA uplink that is necessary for downlink scheduling, link adaptation, hybrid ARQ (automatic repeat request) with soft-combining, and for uplink feedback control signaling. We propose SC-based multiplexing of L1/L2 control signaling with a shared data channel for a set of user equipment (UE) that transmits both an uplink shared data channel and L1/L2 control channel within the same sub-frame. We also propose an L1/L2 control signaling multiplexing scheme without uplink data transmission that takes advantage of frequency hopping using multiple exclusively-assigned time-frequency resources to achieve the frequency diversity effect. Computer simulation results show that the proposed SC-based multiplexing of the L1/L2 control channel with the shared data channel achieves a higher user throughput than multicarrier-based multiplexing. The results also show that the proposed L1/L2 control signaling multiplexing scheme for the UE without uplink data transmission achieves both high quality reception through large frequency diversity and an increase in coverage through full use of the transmission time duration compared to the conventional schemes.

This paper presents the optimum primary- synchronization channel (P-SCH) and secondary-SCH (S-SCH) sequences for the SCH based on criteria to achieve fast initial and neighboring cell search time performance in the Evolved UTRA (E-UTRA) downlink. Simulation results show that the P-SCH sequence has a slight influence on the achievable cell search time, and that the application of multiple sequences, i.e., three P-SCH sequences, is beneficial in achieving fast cell search time performance particularly for the neighboring cell search. The results also show that the Walsh-Hadamard sequence or cyclic-shifted orthogonal sequence is suitable for the S-SCH sequence to indicate the cell ID group. Furthermore, it is shown that the combination of a permutation of the orthogonal S-SCH and P-SCH-specific scrambling sequences is advantageous in suppressing the cross-correlation between S-SCHs that collide and in achieving a fast cell search time particularly for the neighboring cell search in inter-node B synchronous operation.

This paper presents a performance comparison of the initial cell search time and neighboring cell search time using hierarchical and non-hierarchical synchronization channel (SCH) structures in order to establish the optimum SCH structure in the evolved UTRA downlink. Computer simulation results show that in a 19-cell configuration, the cell search time at the 90% cumulative distribution function using the hierarchical SCH structure is less than half that using the non-hierarchical SCH structure in a neighboring cell search under low signal-to-interference plus noise power ratio conditions, although both structures achieve almost the same cell search time in the initial cell search. This is due to the cross-correlation based SCH symbol timing detection in the hierarchical SCH structure, which is affected less by noise than auto-correlation based detection in the non-hierarchical SCH structure. Thus, we conclude that the hierarchical SCH structure is more appropriate than the non-hierarchical SCH structure based on the cell search time performance especially in the neighboring cell search.

This paper proposes a group-wised reference signal (RS) for channel quality indicator measurement in frequency domain channel-dependent scheduling employing adaptive control of the transmission bandwidth in the single-carrier frequency division multiple access-based evolved UMTS terrestrial radio access uplink. In the proposed method, fluctuation in the interference power imparted to the surrounding cells is suppressed to a low level, and both the user throughput for a user equipment (UE) near the cell edge and the cell throughput are improved compared to the conventional uniform RS allocation due to reductions in the error when selecting the optimum UE in channel-dependent scheduling and selecting the modulation and coding scheme in the adaptive modulation and channel coding. Simulation results show that the user throughput at the 5% cumulative distribution function value when employing the proposed group-wised sounding RS allocation with the adaptive transmission bandwidth is increased by approximately 75% and 65% for the inter-site distance of 500 and 1732 m, respectively, compared to that using a uniform RS allocation, while achieving almost the same level of cell throughput.

In the evolved UTRA (UMTS terrestrial radio access) uplink, single-carrier frequency division multiple access (SC-FDMA) radio access was adopted owing to its advantageous low peak-to-average power ratio (PAPR) feature, which leads to wide coverage area provisioning with limited peak transmission power of a set of user equipment (UE). This paper proposes orthogonal pilot channel generation using the combination of FDMA and CDMA in the SC-FDMA-based evolved UTRA uplink. In the proposed method, we employ distributed FDMA transmission for simultaneous accessing users with different transmission bandwidths, and employ CDMA transmission for simultaneous accessing users with identical transmission bandwidths. Moreover, we apply a code sequence with a good auto-correlation property such as a constant amplitude zero auto-correlation (CAZAC) sequence employing a cyclic shift to increase the number of sequences. Simulation results show that the average packet error rate (PER) performance using an orthogonal pilot channel with the combination of FDMA and CDMA in a six-user environment, i.e., four users each with a 1.25-MHz transmission bandwidth and two users each with a 5-MHz transmission bandwidth, employing turbo coding with the coding rate of R = 1/2 and QPSK and 16QAM data modulation coincide well with those in a single-UE environment with the same transmission bandwidth. We show that the proposed orthogonal pilot channel structure using the combination of distributed FDMA and CDMA transmissions and the application of the CAZAC sequence is effective in the SC-FDMA-based evolved UTRA uplink.

In the evolved UTRA (UMTS terrestrial radio access) downlink, orthogonal frequency division multiplexing (OFDM) based radio access was adopted because of its inherent immunity to multipath interference and flexible accommodation of different spectrum arrangements. This paper presents the optimum adaptive modulation and channel coding (AMC) scheme for simultaneously assigned resource blocks (RBs) for the same user when frequency and time domain channel-dependent scheduling is used in the downlink OFDMA radio access with single-antenna transmission. Theoretical analyses and simulation results show that, irrespective of the application of power adaptation to RB-dependent modulation, the improvement in the achievable throughput of the RB-dependent modulation scheme compared to that for the RB-common modulation scheme is slight, i.e., 4 to 5%. In addition, the number of required control signaling bits in the RB-dependent modulation scheme becomes greater than that for the RB-common modulation scheme. Therefore, the authors conclude that the RB-common modulation and channel coding rate scheme is preferred, when multiple RBs of the same coded stream are assigned to one user in the case of single-antenna transmission.

This paper proposes physical channel structures and a cell search method for OFDM based radio access in the evolved UTRA (UMTS Terrestrial Radio Access) downlink, which supports multiple scalable transmission bandwidths from 1.25 to 20 MHz, in the proposed physical channel structures, the central sub-carrier of the OFDM signal is located on the frequency satisfying the 200-kHz raster condition regardless of the transmission bandwidth of the cell site. Moreover, the synchronization channel (SCH) and broadcast channel (BCH), which are necessary for cell search, are transmitted from the central part of the entire transmission spectrum with a fixed bandwidth. In the proposed cell search method, a user equipment (UE) acquires the target cell in the cell search process in the initial or connected mode employing the SCH and possibly the reference signal, which are transmitted from the central part of the given transmission bandwidth. Alter detecting the target cell, the UE decodes the common control information through the BCH, which is transmitted at the same frequency as the SCH, and identifies the transmission bandwidth of the cell to be connected. Computer simulations show the fast cell search time performance using the proposed SCH structure and the cell search method.

This paper proposes an intra-node B orthogonal pilot channel structure employing a sector-specific orthogonal sequence and cell-specific (node B-specific) scrambling code for orthogonal frequency division multiplexing (OFDM)-based radio access in the E-UTRA downlink. This paper also proposes a sophisticated orthogonal pilot channel employing code division multiplexing (CDM) to separate sectored beams and distributed frequency division multiplexing (FDM) to separate streams (transmission antennas) in MIMO channel transmissions simultaneously. Successive simulation results verify the effectiveness of the proposed orthogonal pilot channel structures using distributed FDM among multiple streams and CDM between sectored beams. Furthermore, the simulation results also show that the average packet error rate (PER) performance using the proposed intra-node B orthogonal pilot channel is significantly improved compared to that of the conventional structure employing a random sequence, particularly for 16QAM and 64QAM modulations under high intra-node B interference-to-desired signal power ratio conditions

We recently proposed broadband packet wireless access based on variable spreading factor (VSF)-orthogonal frequency and code division multiplexing (OFCDM) in the forward link and variable spreading and chip repetition factors (VSCRF)-CDMA in the reverse link for the systems beyond IMT-2000. This paper presents experimental evaluations on the throughput performance of that proposed broadband packet wireless access scheme associated with adaptive modulation and channel coding (AMC) in a multipath Rayleigh fading channel employing the implemented base station (BS) and mobile station (MS) transceivers. The implemented OFCDM transceiver verifies the effectiveness of the combination of the OFCDM and AMC including QPSK and 16QAM data modulations with a fast round trip delay of 6 msec for improving the throughput performance by exploiting the frequency diversity effect in a broadband channel. The experimental results show that the throughput performance of 100 and 200 Mbps employing AMC is achieved at the average received signal energy per symbol-to-background noise power spectrum density ratio (E/sub s//N/sub 0/) of approximately 7.5 and 19 dB, respectively, for 15-code multiplexing for the spreading factor of SF=16 in the OFCDM forward link with a 100-MHz bandwidth, in a six-path fading channel with the fading maximum Doppler frequency of f/sub D/=20 Hz. Furthermore, we elucidate that the peak throughput of 20 Mbps is achieved at the average received E/sub s//N/sub 0/of approximately 9 dB by employing QPSK data modulation with R = 1/2 for three-code multiplexing for SF= 4 in a four-path fading channel in the broadband CDMA reverse link with a 40-MHz bandwidth.

This paper compares by computer simulation the throughput performance of a multipath interference canceller (MPIC) and that of a sliding-window chip equalizer (SWCE) in high-speed downlink packet access (HSDPA) in a multipath fading channel. We also propose new MPIC and SWCE configurations that suppress not only multipath interference (MPI) of the downlink shared channel (DSCH) in its own cell but also the multiuser interference (MUI) of the DSCH from a neighboring interference-dominant cell. Computer simulation results elucidate that when the MPIC or the SWCE which suppresses the MPI of the DSCH in only its own cell is employed, the MPIC achieves throughput greater than that of the SWCE ranging from a lower (i.e., the lower average received E/sub b//N/sub 0/) to a higher throughput such as 4.8 Mbit/s, which is achieved by the modulation and coding scheme (MCS) of 16QAM with coding rate R = 1/2. In an even higher throughput region, achieved using the MCS of 16QAM with R = 3/4, the SWCE exhibits superiority over MPIC. Furthermore, we also clarify that with the MPIC and the SWCE with neighboring-cell MUI suppression, the SWCE achieves better throughput compared to the MPIC.

This paper proposes a new parallel-type coherent multistage interference canceller (COMSIC) coupled with multiple-antenna reception (MA-COMSIC) and evaluates the capacity increase in a multipath fading channel in the DS-CDMA reverse link, in order to improve further the channel estimation accuracy and increase the space diversity effect. Simulation results show that the MA-COMSIC with a two block-wise antenna configuration, in which each block has 3 antennas (we denote as (B, D) = (2, 3)), achieved a lower required transmit E/sub b//N/sub 0/ than that with (B, D) = (1, 6) except for extreme cases such as when the number of simultaneous users K exceeds 120 corresponding to K/Pg = 250% (where Pg is the processing gain of 48 = 16/spl times/3). Consequently, even when K = 120, the increase in the required transmit E/sub b//N/sub 0/ of MA-COMSIC with (B, D) = (2, 3) from that in a single-user case is only 1.0 dB owing to the significant improvement in the channel estimation accompanied by the diversity effect. We also elucidate that even when the angle spread among constituent waves in the same path is /spl sigma//sub /spl Lambda/S/ = 5 degrees, the loss of the required transmit E/sub b//N/sub 0/ with (B, D) = (2, 3) for the ideal fading correlation case is suppressed to within 0.5 dB.