This chapter contains sections titled: Introduction Overview of Multicarrier CDMA Systems Channel Model Performance of MC-CDMA System Performance of Overlapping Multicarrier DS-CDMA Systems Performance of Multicarrier DS-CDMA-I Systems Performance of AMC DS-CDMA Systems Performance of SFH/MC DS-CDMA Systems Chapter Summary and Conclusion 
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Overview of Multicarrier CDMA

A comprehensive review on coordinated multi-point operation for LTE-A

The future wireless Fifth Generation (5G) communication network required a higher bandwidth in order to achieve greater data rate. It will be largely characterized by small cell deployments, typically in the range of 200 meters of radius/cell, at most. The implementation of small size networks delivers various advantages such as high data rate and low signal delay. However, it also suffers from various issues such as inter-cell, intra-cell, and inter-user interferences. This paper discusses the issues related to interference management for 5G network from the perspective of Heterogeneous Network and Device-to-Device communication, by using enabling techniques, such as Inter-cell Interference Coordination, Coordinated Multipoint, and Coordinated Scheduling. Furthermore, several pertinent issues have been critically reviewed focusing on their methodologies, advantages and limitations along with the future work. Future directions proposed by the 3rd Generation Partnership Project for interference mitigation has also been outlined. This review will act as a guide for the researchers to comprehend various existing and emerging enabling interference mitigation techniques for further exploration and smooth implementation of 5G wireless network.

Interference management issues for the future 5G network: a review

The invention provides for a method of identifying a cyclic prefix to UEs in an OFDM communication system. The cyclic prefix has a dynamically variable length. The method includes, within an OFDM cell, transmitting MCCH scheduling information in a system information block in an OFDM broadcast channel, and using the MCCH scheduling information to receive the MCCH, wherein the MCCH contains MTCH scheduling information to indicate to the UE which sub-frame carries MTCH.

Transmission of mbms in an ofdm communication system

Electrification turned over a new leaf in aviation by introducing new types of aerial vehicles along with new means of transportation. Addressing a plethora of use cases, drones are gaining attention in the industry and increasingly appear in the sky. Emerging concepts of flying taxi enable passengers to be transported over several tens of kilometers. Therefore, unmanned traffic management systems are under development to cope with the complexity of future airspace, thereby resulting in unprecedented communication needs. Moreover, the long-term increase in the number of commercial airplanes pushes the limits of voice-oriented communications, and future options such as single-pilot operations demand robust connectivity. In this survey, we provide a comprehensive review and vision for enabling the connectivity applications of aerial vehicles utilizing current and future communication technologies. We begin by categorizing the connectivity use cases per aerial vehicle and analyzing their connectivity requirements. By reviewing more than 500 related studies, we aim for a comprehensive approach to cover wireless communication technologies, and provide an overview of recent findings from the literature toward the possibilities and challenges of employing the wireless communication standards. After analyzing the proposed network architectures, we list the open-source testbed platforms to facilitate future investigations by researchers. This study helped us observe that while numerous works focused on cellular technologies to enable connectivity for aerial platforms, a single wireless technology is not sufficient to meet the stringent connectivity demands of the aerial use cases, especially for the piloting operations. We identified the need of further investigations on multi-technology heterogeneous network architectures to enable robust and real-time connectivity in the sky. Future works should consider suitable technology combinations to develop unified aerial networks that can meet the diverse quality of service demands of the aerial use cases.

A Survey of Wireless Networks for Future Aerial Communications (FACOM)

High-altitude platform stations (HAPSs) are expected to provide ultrawide-coverage areas and disaster-resilient networks from the stratosphere at around 20 km by installing wireless equipment on HAPS. Because their altitude is much lower than that of communications satellites, HAPSs can provide mobile communications services directly to smartphones, which are commonly used in terrestrial networks, such as fourth generation Long Term Evolution. Considering the widespread nature of mobile broadband communications and the importance as a backup line in case of disaster, HAPSs are expected to provide a large capacity in the future. A cellular system with single-cell frequency reuse using multiple cells similar to terrestrial mobile communications should be introduced to achieve such a capacity. The number of cells that a HAPS can accommodate ranges from 1 to more than 100, depending on unmanned aerial vehicle (UAV) ability. By contrast, the optimal cell configuration, which depends on the number of available cells, has not been clarified in previous research. In this paper, we propose an optimization method for the cell configuration for HAPS mobile communications using a genetic algorithm, which can be generally applied regardless of the number of cells and can clarify the optimal cell configuration. Although many cells are required to achieve gigabit-class HAPS mobile communications, the heightened power consumption due to the large number of cells is a critical problem for UAVs. Thus, we also investigate the reduction of the total transmission power and demonstrate the feasibility of energy-efficient gigabit HAPS mobile communications with wide coverage.

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System Design of Gigabit HAPS Mobile Communications

Multi-cell cooperative transmission is attracting much attention. This technology improves the cell-edge throughput since multiple base stations cooperate with each other in transmitting signals to the cell-edge user. One basic implementation of multi-cell cooperative transmission is inter-sector cooperation, in which a base station with three sectors uses its own equipment to realize multi-cell cooperative transmission. We extended inter-sector cooperation with our proposal of the sector configuration in which three sectors belonging to the same base station equipment are located at different sites linked by optical fiber. With the sector configuration, users located at cell edges between sites can benefit from the inter-sector cooperation, while users located in areas between sectors can enjoy the merit of inter-sector cooperation via the conventional sector configuration. Our previous studies clarified that inter-sector cooperation with the proposed distributed sector configuration provides superior throughput performance compared to the conventional sector configuration. To clarify the effectiveness of the inter-sector cooperation on the distributed sector configuration, we implemented this function on 3GPP Release 8 LTE-compliant equipment and conducted a field trial with the equipment in Kitakyushu, Fukuoka Prefecture, Japan on March, 2010. In the field trial, we implemented the distributed sector configuration by using RoF and evaluated the multi-cell cooperative transmission. The results of the field trial clarify that multi-cell cooperative transmission can improve cell-edge throughput dramatically.

A Field Trial of Multi-Cell Cooperative Transmission over LTE System

Inter-Cell Interference Coordination (ICIC) is attracting attention recently. In ICIC, cell-edge throughput can be improved by preventing BSs from transmitting signals (hereafter, muting BSs), and the information exchange among BSs is little because each UE is only served by a BS at any instant. However, when a BS is muted, no radio resource is allocated to UEs belonging to the muted BS while UEs belonging to other BSs enjoy high cell-edge throughput. Therefore, there is a possibility that overall cell performance may degrade. To prevent this, we propose a multi-BS cooperative interference control method. The basic concept of the proposed method is that the muting is triggered only when the total throughput of the cooperation area is increased by the muting compared to the total throughput possible without muting. The proposed method makes it possible to increase cell-edge throughput without degrading overall cell performance. We also propose a way to realize this interference control on practical systems. First, we propose a way to realized it on 3GPP Release 8 LTE systems. In the proposed interference control, it is important to estimate throughput (SINR) values with and without muting appropriately. We propose to utilize feedback signals defined in LTE such as Channel Quality Indicator (CQI) and Received Signal Received Power (RSRP) to achieve the accurate throughput estimation. Furthermore, we propose to realize the proposed interference control on a distributed sector configuration using optical fiber systems such as Radio over Fiber (RoF) or Remote Radio Head (RRH). With this configuration, it is possible to achieve ICIC with less burden of information exchange. Especially with three sector configuration, it is possible to achieve "inter-cell" cooperation with "inter-sector" cooperation, which can be easily implemented.

Multi-BS Cooperative Interference Control for LTE Systems

This paper proposes SCS-MC-CDMA system with best effort cell structure. 4th generation mobile communication (4G) system is expected to offer 100 Mbps or higher data rate communication in the high-frequency microwave band. The system is characterized by relatively long delay paths, high maximum Doppler frequency, high power consumption at the mobile terminals and small cell coverage caused by the high data transmission rates and the high-frequency band. All of these are serious problems that must be solved. The proposed SCS-MC-CDMA system can realize high communication quality even under delay spreads as long as a few microseconds and maximum Doppler frequency as high as 1000 Hz. Channel estimation is accurate since code-multiplexed pilot symbols are used, and MMSEC is adopted to reduce inter-code interference. Concerning power consumption, the system can assign a number of sub-carriers, which may be narrower than the whole bandwidth of the system, to each user according to the user's data rate requirements. This lowers the power consumption, especially for low data rate users such as voice users. Moreover, the best effort cell structure overcomes the small cell coverage issue by changing the maximum data rate for each user adoptively according to his distance from the base station or channel quality.

SCS-MC-CDMA system with best effort cell structure

Inter-cell interference coordination (ICIC) is attracting attention recently. This is a technique mainly improving cell-edge throughput by coordinating scheduling and signal transmission of multiple BSs. Different from joint transmission (JT), in which the desired signals for a user equipment (UE) are simultaneously transmitted from multiple BSs, the burdens of information exchange among BSs and its attendant signal processing are mitigated in ICIC because it requires only the exchange of scheduling and control information. In ICIC, the cell-edge throughput is improved by adaptively preventing BSs from transmitting signals (in other words, muting BSs) that would otherwise impose strong interference on the cell- edge UEs in the neighbor cells. Although this improves cell-edge throughput, it may degrade cell overall performance because no radio resource is assigned to UEs belonging to the muted BS. To resolve this issue, we first propose a scheduling method, which enables muting only when the throughput improvement (cell-edge UE) obtained by muting is superior to the total throughput possible without muting. Also, when considering applying this ICIC technique to current commercial systems such as LTE, it should be noted that reference signal, also known as pilot signal, is always transmitted regardless of muting because reference signal is a common signal used for channel estimation. To solve this issue, we also propose a reference signal interference canceller, in which the UE cancels the reference signal being transmitted from the neighbor BS. We evaluate the performance improvement by computer simulations and confirm that cell-edge throughput is dramatically improved by introducing the proposed canceller. We also propose a control algorithm that activates the canceller only when throughput improvement is possible. A basic lab experiment was also conducted to confirm the effect of the proposed interference canceller with 3GPP Rel-8 LTE-compliant equipment.

Atsushi Nagate

Papers

System Design of Gigabit HAPS Mobile Communications

A Field Trial of Multi-Cell Cooperative Transmission over LTE System

Multi-BS Cooperative Interference Control for LTE Systems

SCS-MC-CDMA system with best effort cell structure

Cell Edge Throughput Improvement by Base Station Cooperative Transmission Control with Reference Signal Interference Canceller in LTE System