This paper proposed that a path loss model for outdoor-to-indoor corridor is presented to construct next generation mobile communication systems. The proposed model covers the frequency range of millimeter wave bands up to 40GHz and provides three dimensional incident angle characteristics. Analysis of path loss characteristics is conducted by ray tracing. We clarify that the paths reflected multiple times between the external walls of buildings and then diffracted into one of the buildings are dominant. Moreover, we also clarify how the paths affect the path loss dependence on frequency and three dimensional incident angle. Therefore, by taking these dependencies into consideration, the proposed model decreases the root mean square errors of prediction results to within about 2 to 6dB in bands up to 40GHz.

Technological developments in wireless communication have led to an increasing demand for radio frequencies. This has necessitated the practice of spectrum sharing to ensure optimal usage of the limited frequencies, provided this does not cause interference. This paper presents a framework for managing an unexpected situation in which a primary user experiences harmful interference with regard to database-driven secondary use of spectrum allocated to the primary user towards 5G mobile networks, where the primary user is assumed to be a radar system. In our proposed framework, the primary user informs a database that they are experiencing harmful interference. Receiving the information, the database updates a primary exclusive region in which secondary users are unable to operate in the licensed spectrum. Subsequent to the update, this primary exclusive region depends on the knowledge about the secondary users when the primary user experiences harmful interference, knowledge of which is stored in the database. We assume a circular primary exclusive region centered at a primary receiver and derive an optimal radius of the primary exclusive region by applying stochastic geometry. Then, for each type of knowledge stored in the database for the secondary user, we evaluate the optimal radius for a target probability that the primary user experiences harmful interference. The results show that the more detailed the knowledge of the secondary user's density and transmission power stored in the database, the smaller the radius that has to be determined for the primary exclusive region after the update and the more efficient the spatial reuse of the licensed spectrum that can be achieved.

Massive MIMO is widely recognized as an essential technology for 5G. Together with newly allocated spectrum (bandwidth) and network densification (small cells), it is expected to play a key role in coping with the ongoing explosion in data-traffic demand and services. Compared to 4G MIMO technologies, massive MIMO can offer large gains in cell spectral efficiency, which, in combination with small cells and additional bandwidth, can translate into vast gains in throughput per unit area. We briefly overview the most promising TDD and FDD operation modes for massive MIMO, and discuss their potential benefits and challenges considering operation over different tiers and frequency bands. TDD operation is naturally suited to massive MIMO and can offer “massive MIMO” gains, with simple in-cell processing, low overheads and low end-to-end latencies. We also briefly describe some important massive MIMO activities towards 5G, including standardization efforts, system development and experimental trials.

The dramatic growth in wireless data traffic has triggered the investigation of fifth generation (5G) wireless communication systems. Small cells will play a very important role in 5G to meet the 5G requirements in spectral efficiency, energy savings, etc. In this paper, we investigate low complexity millimeter-wave communication systems with uniform circular arrays (UCAs) in line-of-sight (LOS) multiple-input multiple-output (MIMO) channels, which are used in fixed wireless access such as small cell wireless backhaul for 5G. First, we demonstrate that the MIMO channel matrices for UCAs in LOS-MIMO channels are circulant matrices. Next, we provide a detailed derivation of the unified optimal antenna placement which makes MIMO channel matrices orthogonal for 3×3 and 4×4 UCAs in LOS channels. We also derive simple analytical expressions of eigenvalues and capacity as a function of array design (link range and array diameters) for the concerned systems. Finally, based on the properties of circulant matrices, we propose a high performance low complexity LOS-MIMO precoding system that combines forward error correction (FEC) codes and spatial interleaver with the fixed IDFT precoding matrix. The proposed precoding system for UCAs does not require the channel knowledge for estimating the precoding matrix at the transmitter under the LOS condition, since the channel matrices are circulant ones for UCAs. Simulation results show that the proposed low complexity system is robust to various link ranges and can attain excellent performance in strong LOS environments and channel estimation errors.

Heterogeneous networks (HetNet) with different radio access technologies have been deployed to support a range of communication services. To manage these HetNets efficiently, some interworking solutions such as MIH (media independent handover), ANQP (access network query protocol) or ANDSF (access network discovery and selection function) have been studied. Recently, the millimeter-wave (mm-wave) based HetNet has been explored to provide multi-gigabits-per-second data rates over short distances in the 60GHz frequency band for 5G wireless networks. WiGig (Wireless Gigabit Alliance) is one of the available radio access technologies using mm-wave. However, the conventional interworking solutions are not sufficient for the implementation of LTE (Long Term Evolution)/WiGig HetNets. Since the coverage area of WiGig is very small due to the high propagation loss of the mm-wave band signal, it is difficult for UEs to perform cell discovery and handover if using conventional LTE/WLAN (wireless local area networks) interworking solutions, which cannot support specific techniques of WiGig well, such as beamforming and new media access methods. To solve these problems and find solutions for LTE/WiGig interworking, RAN (radio access network)-level tightly coupled interworking architecture will be a promising solution. As a RAN-level tightly coupled interworking solution, this paper proposes to design a LTE/WiGig protocol adaptor above the protocol stacks of WiGig to process and transfer control signaling and user data traffic. The proposed extended control plane can assist UEs to discover and access mm-wave BSs successfully and support LTE macro cells to jointly control the radio resources of both LTE and WiGig, so as to improve spectrum efficiency. The effectiveness of the proposal is evaluated. Simulation results show that LTE/WiGig HetNets with the proposed interworking solution can decrease inter-cell handover and improve user throughput significantly. Moreover, the downlink backhaul throughput and energy efficiency of mm-wave HetNets are evaluated and compared with that of 3.5GHz LTE HetNets. Results indicate that 60GHz mm-wave HetNets have better energy efficiency but with much heavier backhaul overhead.

Millimeter-wave (mmw) frequency bands, especially 60GHz unlicensed band, are considered as a promising solution for gigabit short range wireless communication systems. IEEE standard 802.11ad, also known as WiGig, is standardized for the usage of the 60GHz unlicensed band for wireless local area networks (WLANs). By using this mmw WLAN, multi-Gbps rate can be achieved to support bandwidth-intensive multimedia applications. Exhaustive search along with beamforming (BF) is usually used to overcome 60GHz channel propagation loss and accomplish data transmissions in such mmw WLANs. Because of its short range transmission with a high susceptibility to path blocking, multiple number of mmw access points (APs) should be used to fully cover a typical target environment for future high capacity multi-Gbps WLANs. Therefore, coordination among mmw APs is highly needed to overcome packet collisions resulting from un-coordinated exhaustive search BF and to increase total capacity of mmw WLANs. In this paper, we firstly give the current status of mmw WLANs with our developed WiGig AP prototype. Then, we highlight the great need for coordinated transmissions among mmw APs as a key enabler for future high capacity mmw WLANs. Two different types of coordinated mmw WLAN architecture are introduced. One is distributed antenna type architecture to realize centralized coordination, while the other is autonomous coordination with the assistance of legacy Wi-Fi signaling. Moreover, two heterogeneous network (HetNet) architectures are also introduced to efficiently extend the coordinated mmw WLANs to be used for future 5th Generation (5G) cellular networks.

This contribution addresses optimum wireless link selection in a 5G heterogeneous Multicomm environment in which multiple distinct Radio Access Technologies can be operated simultaneously by a given Mobile Device. The related decision making mechanisms are proposed to be part of the Mobile Device User Equipment which identifies the preferred Radio Access Technologies to be operated as well as the preferred Modulation and Coding parameters and finally selects the optimum choice either independently or through negotiation with the Network Infrastructure Equipment. In this context, the concerned Mobile Device is able to manage the bandwidth to be employed for communication — the bandwidth per Radio Access Technology is typically defined by the Network Infrastructure but the possibility for aggregating a multitude of distinct technologies introduces a new degree of freedom enabling the choice of the bandwidth selection. Simulation results demonstrate that the Mobile Device driven selection of a Multicomm configuration may either substantially reduce Mobile Device power consumption (75% in a typical example) or increase the aggregate throughput at an identical power consumption level compared to the single link case (a 3x factor in a typical example).

In order to tackle the rapidly increasing traffic, the 5th generation (5G) mobile communication system will introduce small cells using higher frequency bands with wider bandwidth to achieve super high bit rate transmission of several tens of Gbps. Massive multiple input multiple output (MIMO) beamforming (BF) is promising as one of the technologies that can compensate for larger path-loss in the higher frequency bands. Joint analog fixed BF and digital precoding have been proposed to reduce the cost of a Massive MIMO transceiver. However, the conventional scheme assumes the transmission of a few streams using well-known codebook-based precoding as the digital precoding, and both a selection method of the fixed BF weights and a digital precoder design, which are suitable for super high bit rate transmission using multiple streams, have not been studied. This paper proposes a joint fixed BF and CSI-based precoding (called FBCP) scheme for the 5G Massive MIMO systems. FBCP first selects the analog fixed BF weights based on a maximum total received power criterion, and then it calculates an eigenmode (EM) precoding matrix by exploiting CSI. This paper targets a 5G system achieving over 20Gbps in the 20GHz band as one example. Throughput performances of the Massive MIMO using the proposed FBCP are evaluated by link level simulations using adaptive modulation and coding and it is shown that the proposed FBCP with the optimum number of selected beams (baseband chains) can use higher level modulation, up to 256QAM, and higher coding rates and achieve throughputs close to 30Gbps while the cost and complexity can be reduced compared with the fully digital Massive MIMO.

Currently, many operators worldwide are deploying Long Term Evolution (LTE) to provide much faster access with lower latency and higher efficiency than its predecessors 3G and 3.5G. Meanwhile, the service rollout of LTE-Advanced, which is an evolution of LTE and a “true 4G” mobile broadband, is being underway to further enhance LTE performance. However, the anticipated challenges of the next decade (2020s) are so tremendous and diverse that there is a vastly increased need for a new generation mobile communications system with even further enhanced capabilities and new functionalities, namely a fifth generation (5G) system. Envisioning the development of a 5G system by 2020, at DOCOMO we started studies on future radio access as early as 2010, just after the launch of LTE service. The aim at that time was to anticipate the future user needs and the requirements of 10 years later (2020s) in order to identify the right concept and radio access technologies for the next generation system. The identified 5G concept consists of an efficient integration of existing spectrum bands for current cellular mobile and future new spectrum bands including higher frequency bands, e.g., millimeter wave, with a set of spectrum specific and spectrum agnostic technologies. Since a few years ago, we have been conducting several proof-of-concept activities and investigations on our 5G concept and its key technologies, including the development of a 5G real-time simulator, experimental trials of a wide range of frequency bands and technologies and channel measurements for higher frequency bands. In this paper, we introduce an overview of our views on the requirements, concept and promising technologies for 5G radio access, in addition to our ongoing activities for paving the way toward the realization of 5G by 2020.

The fifth generation (5G) mobile communication technologies are attracting a lot of attention in terms of accommodating the huge traffic expected in the future. Millimeter wave communications, which utilize wide frequency bands, are attracting attention for the realization of the high capacity required in the 5G era. In millimeter wave communications, beamforming with massive antennas is expected to play a very important role in compensating the large propagation loss of millimeter waves. Because massive beamforming yields narrow beams, the search for the optimal beam could have considerable impact on the system. In this paper, we propose a new beam search method that can reduce the load of beam search significantly while keeping beamforming gain almost the same as that of the conventional method. The proposed method consists of three stages with the creation of a set of candidate beams in the first stage, selection of an initial beam in the second stage, and refinement of the selected beam in the third stage. In the first stage, the created set of candidate beams contains beams of various widths instead of beams of a uniform width to reduce the number of candidate beams in the set. Here, we leverage the property of millimeter waves according to which the fluctuation of millimeter wave propagation loss is spatially and temporally small because of the fewer multipaths, and therefore, the propagation loss has strong correlation with the user location. By using the decreased set of candidate beams, the beam search time can be reduced in the second stage. Then the beam refinement can increase the beamforming gain to increase user throughput in the third stage. To confirm the effects of the proposed beam search method, we conduct system level simulations by using a propagation model for millimeter wave communications proposed by MiWEBA, which is an international project between Europe and Japan. The results show that the proposed beam search method can reduce the number of candidate beams, and can therefore shorten the beam search time by about 39% without any degradation in outage probability compared with a conventional method.

Non-orthogonal multiple access (NOMA) utilizing the power domain and advanced receiver has been considered as one promising multiple access technology for further cellular enhancements toward the 5th generation (5G) mobile communications system. Most of the existing investigations into NOMA focus on the combination of NOMA with orthogonal frequency division multiple access (OFDMA) for either downlink or uplink. In this paper, we investigate NOMA for uplink with single carrier-frequency division multiple access (SC-FDMA) being used. Differently from OFDMA, SC-FDMA requires consecutive resource allocation to a user equipment (UE) in order to achieve low peak to average power ratio (PAPR) transmission by the UE. Therefore, sophisticated designs of scheduling algorithm for NOMA with SC-FDMA are needed. To this end, this paper investigates the key issues of uplink NOMA scheduling such as UE grouping method and resource widening strategy. Because the optimal schemes have high computational complexity, novel schemes with low computational complexity are proposed for practical usage for uplink resource allocation of NOMA with SC-FDMA. On the basis of the proposed scheduling schemes, the performance of NOMA is investigated by system-level simulations in order to provide insights into the suitability of using NOMA for uplink radio access. Key issues impacting NOMA performance are evaluated and analyzed, such as scheduling granularity, UE number and the combination with fractional frequency reuse (FFR). Simulation results verify the effectiveness of the proposed algorithms and show that NOMA is a promising radio access technology for 5G systems.

5G is the next step in the evolution of mobile communication and a key component of the future networked society. It will include the evolution of LTE as well as new non-backwards-compatible technology. 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. Key technology components include operation at higher frequency bands and flexible spectrum usage, advanced multi-antenna/multi-site transmission, lean transmission, access/backhaul integration, and possibility for direct device-to-device communication.

Millimeter-wave (mm-wave) radio is attracting attention as one of the key enabling physical layer technologies for the fifth-generation (5G) mobile access and backhaul. This paper aims at clarifying possible roles of mm-wave radio in the 5G development and performing a comprehensive literature survey on mm-wave radio channel modeling essential for the feasibility study. Emphasis in the literature survey is laid on grasping the typical behavior of mm-wave channels, identifying missing features in the presently available channel models for the design and evaluation of the mm-wave radio links within the 5G context, and exemplifying different channel modeling activities through analyses performed in the authors' group. As a key technological element of the mm-wave radios, reduced complexity beamforming is also addressed. Design criteria of the beamforming are developed based on the spatial multipath characteristics of measured indoor mm-wave channels.

Triggered by the explosion of mobile traffic, 5G (5th Generation) cellular network requires evolution to increase the system rate 1000 times higher than the current systems in 10 years. Motivated by this common problem, there are several studies to integrate mm-wave access into current cellular networks as multi-band heterogeneous networks to exploit the ultra-wideband aspect of the mm-wave band. The authors of this paper have proposed comprehensive architecture of cellular networks with mm-wave access, where mm-wave small cell basestations and a conventional macro basestation are connected to Centralized-RAN (C-RAN) to effectively operate the system by enabling power efficient seamless handover as well as centralized resource control including dynamic cell structuring to match the limited coverage of mm-wave access with high traffic user locations via user-plane/control-plane splitting. In this paper, to prove the effectiveness of the proposed 5G cellular networks with mm-wave access, system level simulation is conducted by introducing an expected future traffic model, a measurement based mm-wave propagation model, and a centralized cell association algorithm by exploiting the C-RAN architecture. The numerical results show the effectiveness of the proposed network to realize 1000 times higher system rate than the current network in 10 years which is not achieved by the small cells using commonly considered 3.5GHz band. Furthermore, the paper also gives latest status of mm-wave devices and regulations to show the feasibility of using mm-wave in the 5G systems.

As new systems and applications are introduced for next-generation wireless systems, the propagation channels in which they operate need to be characterized. This paper discusses propagation channels for four types of next-generation systems: (i) distributed Multiple-Input Multiple-Output (MIMO) and Cooperative MultiPoint (CoMP) systems, which require the characterization of correlation between channels from a mobile station to different base stations or access points; (ii) device-to-device communications, where propagation channels are characterized by strong mobility at both link ends (e.g., in vehicle-to-vehicle communications), and/or significant impact of moving shadowing objects; (iii) full-dimensional MIMO, where antenna arrays extend in both the horizontal and vertical dimension, so that azimuthal and elevation dispersion characteristics of the channel become relevant, and (iv) millimeter wave Wireless Local Area Network (WLAN) and cellular communication systems, where the high carrier frequency leads to a change (compared to microwave communications) concerning which propagation processes are dominant. For each of these areas, we give an overview of measurements and models for key channel properties. A discussion of open issues and possible future research avenues is also provided.

This Letter employs transmission-line theory for the impedance-matching circuits for a single-chip power amplifier (PA) and verifies for 5 GHz-band wireless LAN (IEEE 802.11a) applications. The presented matching circuits are composed of conductor-backed coplanar waveguide (CPW) meander-line resonators and impedance (K) inverters. One of the advantages of the presented circuits is that it can save on-chip space occupied by the matching circuits compared to that using the spiral inductors, thus reducing the cost. The prototype chip, which consists of PA and matching circuits, is designed employing the presented theory and fabricated. A few of the measured results to verify the design theory are presented.

Devices DC, RF, and microwave power performances between Al0.3Ga0.7As/In0.15Ga0.85As double doped-channel FET (D-DCFETs), conventional doped-channel FETs (DCFETs) and HEMTs are compared with each other. Device linearity and power performance have been improved by a double doped-channel design. The D-DCFETs provides a higher current density, higher gate breakdown voltage, and improves gate operation bias range as well as frequency performance. The linear power gain and output power for D-DCFETs is 19 dB and 305 mW/mm with a power-added efficiency of 52% at Vds = 2.5 V under a 1.9 GHz operation. These advantages suggest that double doped-channel design is more suitable for a high linearity and high microwave power device applications.