Frequency Utilization Efficiency Research Articles

Two-Step Channel Observation Scheme Considering Spread of Observation Results in Dynamic Spectrum Sharing

Dynamic Spectrum Sharing (DSS), in which multiple wireless systems share the same radio resource, has been studied to improve frequency utilization efficiency. In DSS, the channel occupation ratio (COR), the usage of radio resources (channels) used by other wireless systems, is measured. The wireless system dynamically selects the channel with the lowest COR for communication. A long observation time is required to measure the COR with high accuracy. However, as the number of observed channels increases, the observation time per channel becomes shorter. Since the shorter observation time, the degradation of the accuracy of observed COR is a problem. This paper proposes a two-step channel observation scheme considering the spread of observed results. In the first observation, the proposed scheme measures all channels and excludes channels with high COR, considering the spread due to the error in the observed results. Only remaining channels are observed in the second observation, so the observation time can be relatively long. Computer simulation results show that the proposed scheme with 200 ms or more of first observation can improve communication reliability compared to the conventional scheme.

Advanced OTFS communication system with compact spectrum and power efficiency improvement

SummaryOrthogonal time frequency space (OTFS) modulation technique is one‐step more precoded system of the conventional orthogonal frequency division multiplexing (OFDM) system, i.e., a double precoded system. The OTFS system was suggested especially for the robust and reliable high‐speed vehicle communications and massive multiple‐input multiple‐output (MIMO) systems. Nevertheless, this basic OTFS system has serious problems: high out‐of‐band (OOB) power emission and high peak‐to‐average power ratio (PAPR). This high OOB power spectrum requires a very wide guard band that can produce a great loss of frequency utilization efficiency, and the power efficiency becomes very poor due to this high PAPR problem. Therefore, in this paper, in order to mitigate these drawbacks, an advanced OTFS communication system is proposed to show the compact OOB power spectrum and power efficiency improvement. This system can be designed by discrete Fourier transform (DFT)‐spread windowing and restructuring‐OTFS (DFT‐Spread WR‐OTFS) scheme that can reduce PAPR by 2.1 dB, 0.5 dB, 1.7 dB, and 1.8 dB compared to the conventional OFDM, DFT‐Spread OFDM, basic OTFS and WR‐OTFS schemes, respectively. Consequently, the efficiency of the high power amplifier (HPA) is improved due to the low PAPR of the proposed system. In addition, we comprehensively evaluate the impact of PAPR reduction performance on the OOB power spectrums and bit error rate (BER) performance of each system in HPA linear and nonlinear environments. Simulation results verify that the power spectrums and the BER performance of the proposed system are better than the conventional schemes in HPA nonlinear environments.

Interference Handling Challenges toward Full Duplex Evolution in 5G and Beyond Cellular Networks

Full duplex is a scheme that changes the duplexing paradigm in wireless communication networks. Enabled by self-interference cancellation methodology, it unlocks the potential to improve frequency utilization efficiency and reduce resource allocation latency. However, embracing the full duplex scheme in a mobile network can lead to complications in terms of cross-link interference among network entities. As a matter of fact, a successful network integration for the scheme must consider handling these emerging types of interference. On the other hand, diversification in evolving 5G networks - struggling to address unprecedented broad demands - allows the opportunity to consider full duplex operation at a newly emerging network entity type, which is the integrated access and backhaul (IAB) node. Indeed, this might be the beginning of a network adoption series for the scheme. For instance, the non-terrestrial network, another newly emerging use case, can be the next to benefit from full duplex resource utilization. On the matter of standardized solutions, 3GPP has specified several cross-link interference handling mechanisms, which eases the integration process of the scheme at the network infrastructure level, and paves the way for later phases of user equipment adoption. This incremental network adoption ensures the required technological maturity of self-interference cancellation. In practical terms, self-interference cancellation requirements depend on device type and its deployment environment. As the environment defines the properties of the self-interference channel, it must be known to the self-interference canceller. To assess the full duplex adoption feasibility in the IAB use case, we present experimental study outcomes of self-interference channel measurement addressing the outdoor deployment scenario of an IAB node.

Self-adaptive power control with deep reinforcement learning for millimeter-wave Internet-of-vehicles video caching

Video delivery and caching over the millimeter-wave (mmWave) spectrum is a promising technology for high data rate and efficient frequency utilization in many applications, including distributed vehicular networks. However, due to the short handoff duration, calibrating both optimal power allocation of each base station toward its associated vehicles and cache allocation are challenging for their computational complexity. Heretofore, most video delivery applications were based on on-line or off-line algorithms, and they were limited to compute and optimize high dimensional objectives within low-delay in large scale vehicular networks. On the other hand, deep reinforcement learning is shown for learning such scale of a problem with an optimized policy learning phase. In this paper, we propose deep deterministic policy gradient-based power control of mmWave base station (mBS) and proactive cache allocation toward mBSs in distributed mmWave Internet-of-vehicle (IoV) networks. Simulation results validate the performance of the proposed caching scheme in terms of quality of the provisioned video and playback stall in various scales of IoV networks.

Adaptive Channel Selection and Transmission Timing Control for Simultaneous Receiving and Sending in Relay-Based UAV Network

Recently, the demand for technology that can wirelessly transmit images taken by unmanned aerial vehicles (UAVs) has increased. Relay transmission technology is attracting particular attention, as it can provide wireless transmission to remote locations even in environments lacking infrastructure. Here, we focus on further developing an existing relay transmission system, namely, the simultaneous reception and transmission method, using multiple frequency bands. In this method, a relay node receives data from a source node and simultaneously transmits data to a destination node using another channel. This technology has the advantages of high frequency utilization efficiency and a short transmission time; however, buffer overflow at the relay node may remain, which could contribute to video quality degradation. Thus, we propose a buffer control method involving two proposed elements: a channel selection method, and a transmission start timing control method. By applying these two methods, we show that the buffer overflow rate at the relay node is decreased, and the amount of data that can be received by the destination node is maximized within the assigned sub frame. Ultimately, these results can contribute to improving the quality of videos transmitted in real-time using relay transmission with UAVs.

Novel Unmanned Aerial Vehicle-Based Line-of-Sight MIMO Configuration Independent of Transmitted Distance Using Millimeter Wave

Recently, the millimeter-wave band has been used in outdoor wireless communications to improve the frequency utilization efficiency. In this study, we propose a method to realize line-of-sight multiple-input multiple-output (LOS-MIMO) transmission independent of the transmitted distance using a two-dimensional (2-D) fixed antenna element arrangement, assuming millimeter-wave-band communication by small autonomous unmanned aerial vehicles. In conventional LOS-MIMO transmission with uniformly spaced antenna elements, the theoretical upper bound of the channel capacity is obtained, which decreases at a certain transmitted distance. Therefore, we focus on the fact that the propagation channel characteristics in pure LOS are geometrically determined by the transmitted distance, and consider the optimization of the arrangement of antenna elements. The element arrangement is fixed without using antenna selection from the viewpoint of system simplification. In addition, from the viewpoint of array size, we study the optimization corresponding to a 2-D element arrangement. The proposed method approximates the optimal arrangement from a vast number of 2-D element arrangements using a genetic algorithm. We evaluate the channel capacity characteristics of the proposed method by computer simulation and show that the characteristic degradation due to change in the transmitted distance in conventional LOS-MIMO transmission is improved. In addition, we evaluate a $4\times4$ MIMO transmission in an outdoor environment. The $4\times4$ MIMO propagation channel is also measured by an actual measurement equipment in the 66-GHz band and it is shown that the measured and calculated results agree with each other.

Sequence-Based Unicast in Wireless Sensor Networks

We consider a single-hop wireless sensor network in which each sensor node has an individual elastic data stream to transmit to each other node. We refer to this traffic pattern as unicast in this paper. The network has multiple slotted channels available for the data transmissions. To guarantee successful unicast within a bounded delay, we consider deterministic schemes that pre-assign each node a periodic schedule sequence to schedule transmitting and receiving at each time slot. The sequence period should be minimized since it upper bounds the unicast delay. We have investigated both synchronous TDMA sequences and asynchronous sequences. Since accurate time synchronization is difficult to achieve in sensor networks, we mainly present analysis and design for asynchronous sequences. In this paper, for a group-based channel assignment, we present a lower bound on the common period and propose a sequence construction method by which the period can achieve the same order as the lower bound. We also analyze optimal transmitting and receiving probabilities for two random schemes and compare their frequency utilization efficiency. Finally, unicast delay and energy consumption performance are compared by simulations.

Virtual Cell Based Resource Allocation for Efficient Frequency Utilization in Unmanned Aircraft Systems

Recently, unmanned aircraft systems (UASs) have attracted attention as a new avenue for commercial services. Using the flexible mobility of unmanned aircrafts (UAs), commercial services can be operated in wide areas. However, there is a problem in the wireless communication between the UA and its ground station. When several UASs are operated within the neighboring airspace, wireless-communication conflicts occur. One of the most effective solutions for this issue is to decide the communication schedule using a time-division multiple access (TDMA) scheme. Furthermore, by spatially reusing the time slot, numerous UAs can be operated within the neighboring airspace, in a limited frequency band. In this paper, we propose an efficient time-slot allocation for enhancing the frequency resource utilization. Our proposed scheme determines the time-slot allocation considering the time-slot spatial reuse, using a virtual cell based space partitioning method. In addition, we consider the influence of the UA mobility on the network to decide the parameters for the proposed resource allocation system. The effectiveness of our proposed resource allocation is evaluated through computer-based simulation.

Spectral Efficiency Maximization of Grouped Routing Optical Networks With Shared Protection

Reliable coarse granular routing optical network architectures that maximize fiber frequency utilization efficiency are presented. The architectures combine coarse granular routing and fine granular add/drop operations, where optical paths are carried by virtual optical pipes. Higher efficiency than conventional fine granular routing networks is achieved by dense path packing in the frequency domain. We propose two architectures that apply shared protection with different levels of granularity and develop static network design algorithms for the two different shared protection schemes. The design algorithms neutralize the impairment caused by adjacent path dropping in the frequency domain. Numerical experiments verify that the necessary number of fibers in a network can be reduced by up to 20% due to the improved spectral utilization efficiency.

Group buying spectrum auction algorithm for fractional frequency reuse cognitive cellular systems

Fractional frequency reuse (FFR) can not only coordinate inter-cell interference (ICI), but also improve communication quality of cell-edge users, whose key idea is to make a tradeoff between frequency utilization efficiency improvement and ICI suppression. In terms of the fact that conventional spectrum auction neglects the inter-cell and intra-cell interference and wireless spectrum has become scarce resources in cognitive radio networks, in this paper, FFR technology is introduced into the field of spectrum auction and a group reuse spectrum auction mechanism for FFR (GRSAF) is proposed in cognitive cellular systems to achieve higher spectrum allocation and usage efficiency. A Lagrangian relaxation (LR) algorithm is developed to solve the optimal sum utility maximization spectrum allocation problem. Simulation results show that the GRSAF mechanism can significantly improve the sum utility, spectrum reusability as well as satisfaction degree of buyers compared with other two existing auction mechanisms.

초연결 시대의 UAS 주파수의 효율적 활용방안

초연결 시대의 UAS 주파수의 효율적 활용방안

Iterative estimation of undesired signal power for superposed multicarrier transmission with channel estimation error

Superposed multicarrier transmission scheme is known to improve frequency utilization efficiency when several wireless systems share the same spectrum. To suppress the effect of interference, forward error correction (FEC) metric masking is proposed. In this technique, the log-likelihood ratio (LLR) that corresponds to the superposed band is set to zero, because received bits that correspond to the superposed band are unreliable. However, to apply FEC metric masking, the information about superposed band must be known at the receiver beforehand. Furthermore, the received bits contain channel estimation errors, which are the cause of performance degradation. In this paper, we propose an iterative estimation technique for undesired signal power (noise, interference, and channel estimation error) for superposed multicarrier transmission. We use the estimated power of the undesired signal to calculate the LLR that takes the channel estimation error into account, since including this extra information about the channel improves the bit error rate (BER). The proposed scheme estimates the power of undesired signal on each subcarrier, and thus, the information about superposed band is not required. Simulation results show that the accuracy of estimating undesired signal becomes more reliable as the number of estimations increases, so that BER becomes better as a result of iterative estimation.

Large time-bandwidth product OFDM chirp waveform diversity using for MIMO radar

Multiple-input multiple-output radar waveform diversity design has received much attention, but many of existing waveforms are lack of a large time-bandwidth product. This paper proposes an orthogonal frequency division multiplexing (OFDM) chirp waveform diversity design scheme to generate four waveforms with good correlation properties, ambiguity performance and Doppler tolerance. The method jointly utilizes classic chirp waveform and OFDM to conduct multi-carrier modulation. This scheme enables us to exploit full bandwidth for each waveform and thus has an high frequency utilization efficiency. The modulation and demodulation of the four OFDM chirp waveforms are presented. The performance of the designed waveforms is analyzed by the correlation and ambiguity functions. Simulation results validate that our proposal can generate more orthogonal waveforms without significant performance degradation.

Stochastic learning automata‐based channel selection in cognitive radio/dynamic spectrum access for WiMAX networks

SummaryThis paper proposes a cognitive radio‐based dynamic bandwidth allocation scheme for secondary users in a cluster‐based WiMAX network. It uses a learning automata‐based algorithm to find the optimal transmission channel, while ensuring minimum channel loss and a considerably high signal‐to‐noise ratio, and concurrently minimizing costly channel switching activities when primary users request licensed channels. The objective is to coordinate efficient frequency utilization and frequency reusability in each of the clusters in the network and to make data transmission possible without depleting the spectrum. The proposed scheme subsumes unforeseen channel faults into the channel feedback and decides the optimal channel. The system converges asymptotically to an ϵ‐optimal solution. Copyright © 2014 John Wiley & Sons, Ltd.

DVB-T2기반으로 지상파 UHDTV방송과 직접수신환경 구축 연구

In this paper, 4K-UHDTV or 8K-UHDTV and UHD-3DTV that the next generation broadcasting implementation and the possibility of direct receiving environment construction is analyzed on the terrestrial broadcasting. Particularly, we investigated the possibility by analyzing the previous and related works with regard to UHDTV transmission by DVB-T2 that is one of the best commercialized transmission mode. In order that the UHDTV broadcasting succeeds once again after completion of digital terrestrial switch over at the end of 2012, the ultra high resolution image transfer is important. However, the direct, the indoor and ubiquitous receiving environment is important in not only TV but also the personal type multimedia terminal in the sense of UHDTV service penetration. Therefore, in this paper, by using SFN and high error-correcting mode in DVB-T2 standard, the efficient frequency utilization and effective reception environment construction is illustrated. Particularly, SFN network constitution by 2 mutually different frequencies including the VHF bandwidth and UHF band, and etc. is shown. And the method that builds the free wireless receive environment by using SFN low power radio repeater and for home use gap filler is proposed. And the effect and frequency amount required are presented, when UHDTV broadcasting use 10MHz bandwidth.

LTE/LTE-Advanced 시스템간 채널 간섭분석을 통한 주파수 공유 연구

3GPP의 LTE/LTE-Advanced 시스템은 OFDM(Orthogonal Frequency Division Multiplexing) 기술적용으로 주파수 할당에 의한 간섭분석 및 주파수 공유평가가 중요하다. 이에 본 논문에서는 LTE 두 사업자/시스템간의 인접채널 간섭 분석에 의한 주파수 공유연구를 수행하였다. 업링크 및 다운링크에서의 시스템 용량 및 스루풋(throughput) 손실에 대한 시뮬레이션 분석이 이루어져 5% 손실율의 주파수 공유기준으로 요구되는 ACIR(Adjacent Channel Interference Ratio) 값을 정의하였다. 유저(user)의 위치, 간섭 대역폭, 시스템 분리 옵셋(separation offset) 등의 파라미터들에 의해 주파수 공유를 위해 요구되는 ACIR 값에 미치는 영향이 분석되었으며, 이러한 결과 데이터 및 간섭분석 방법들은 향후 LTE RF 표준 및 주파수 유효이용에 참고자료로 활용될 것이다. Since OFDM(Orthogonal Frequency Division Multiplexing) technology is applied into LTE(Long Term Evolution)/LTE-Advanced system, it is important to estimate the spectrum sharing and to analyze interference in LTE system based on the characteristics of frequency assignment. Therefore, in this paper, a study on the adjacent channel interference between two operators/systems to provide LTE services. For co-existence of LTE systems, the relative capacity loss and the relative throughput loss in uplink and downlink have been simulated to evaluated ACIR(Adjacent Channel Interference Ratio) values with 5% loss rate. Some parameters such as the location of user, aggressor bandwidth, and the separation offset affect the required ACIR value for spectrum sharing, and these results and interference analysis schemes in this article can provide reliable reference for LTE RF standardization and efficient frequency utilization in future.

30-Gb/s Bidirectional Transparent Optical Transmission With an MMF Access and an Indoor Optical Wireless Link

This letter describes a 30-Gb/s bidirectional transparent optical transmission, over a 4.4-km multimode fiber (MMF) in combination with an indoor optical wireless (OW) link, which could provide limited mobility. Due to MMF's advantages, such as lower installation costs and easy maintenance, it is used as the access link. To enhance the MMFs bandwidth and provide the feasibility to use standard single-mode devices in the OW terminal (OWT), center launching and center detection techniques are both utilized. The stability of the indoor OW channel and the modal noise in MMF are investigated. Discrete multitone modulation with power and bit loading algorithms are applied to improve system's frequency utilization efficiency and robustness.

Spectrum Suppressed Transmission Scheme for Higher Frequency Utilization Efficiency

Spectrum Suppressed Transmission Scheme for Higher Frequency Utilization Efficiency

Direct Spectrum Division Transmission for Highly Efficient Frequency Utilization in Satellite Communications

Direct Spectrum Division Transmission for Highly Efficient Frequency Utilization in Satellite Communications

무선통신과 임베디드 제어시스템 통신환경의 채널특성 알고리즘에 관한 연구

무선통신 임베디드시스템 및 MIMO 전파특성 예측을 위해 실내 및 실외 전파 예측 프로그램을 통합하여 하나의 시뮬레이터를 통해 실내 외 전파 예측이 가능하다. 이러한 해석 기법 개발을 통하여 여러 송신기간의 간섭 문제 및 최대 송신거리 문제, 주파수 이용 효율 등 여러 가지 문제에 대한 분석 및 예측이 가능해진다. 본 예측 기술 개발에서는 기존의 Walfish-Ikegami 방법 등 간략화된 모델보다 정확도 높으면서도 환경적 특성을 잘 고려 할 수 있는 광선추적법을 구현한 모의해석 소프트웨어를 개발하고 효율적인 광선 추적이 가능하도록 고안된 광선 추적 기법과 추적된 광선 정보를 이용하여 전파 특성 해석 기술을 접목시켜 효율적이면서도 이론적 특성을 잘 반영한 전파 특성 예측 기술을 확보하였다. 또한 주파수 확보를 위한 국내 임베디드시스템 및 IMT-Advanced용 신규대역 확보를 위한 주파수 특성 및 IMT-Advanced용 주파수인 3-5GHz대역 전파특성을 규명하여 국내 무선통신 기술 개발에 필요한 기반 기술 확보 및 전파간섭등 주파수 관리 기술 확보를 위하여 검증 및 실험을 통하여 확인 하였다. MIMO wireless communication embedded systems, and for propagation prediction for indoor and outdoor propagation prediction program incorporates an indoor/outdoor propagation through the simulator can be predicted. This analysis technique developed by the interference between multiple transmitters and a maximum transmission distance issues, the frequency utilization efficiency for a variety of issues, including analysis and prediction becomes possible. Development of the prediction of the conventional methods, but I can consider the environmental characteristics of the ray tracing simulation software to develop and implement an efficient ray tracing, ray tracing techniques and are designed to enable tracked beam analysis of propagation characteristics using information technology by combining the theoretical characteristics of an efficient and well-reflected propagation prediction technique was employed. The frequency of domestic embedded systems, ensure the frequency characteristics and frequency of 3-5GHz band for propagation to investigate the development of local wireless communication technology-based skills needed for securing and jeonpaganseopdeung frequency management techniques to ensure the verification and verified through experiments.