Current Channel State Research Articles

Comparative Performanceof Subcarrier Schedulers in Uplink LTE-A under High Users’ Mobility

This paper evaluates the effects of high mobility of Users Equipment (UEs) on the performances of different data rate services using four scheduling algorithms in the uplink of LTE system using the uplink Vienna simulator.The uplink reports Channel Quality Indicator (CQI), Precoding Matrix Indicator (PMI) and Rank Indicator (RI) to inform the evolved node base station (eNodeB or eNB) about the current channel state. We simulate 20 and 30 UEs switch at high mobility and different service demands. Simulation results show that under 100 kmh -1 speed the Best CQI and Proportional Fair schedulers are the best in performance for low delay and the Round Robin algorithm is the worst scheduling algorithm among other schedulers.

Visible Light Communications towards 5G

5G networks have to offer extremely high capacity for novel streaming applications. One of the most promising approaches is to embed large numbers of cooperating small cells into the macro-cell coverage area. Alternatively, optical wireless based technologies can be adopted as an alternative physical layer offering higher data rates. Visible light communications (VLC) is an emerging technology for future high capacity communication links (it has been accepted to 5GPP) in the visible range of the electromagnetic spectrum (~370–780 nm) utilizing light-emitting diodes (LEDs) simultaneously provide data transmission and room illumination. A major challenge in VLC is the LED modulation bandwidths, which are limited to a few MHz. However, myriad gigabit speed transmission links have already been demonstrated. Non line-of-sight (NLOS) optical wireless is resistant to blocking by people and obstacles and is capable of adapting its’ throughput according to the current channel state information. Concurrently, organic polymer LEDs (PLEDs) have become the focus of enormous attention for solid-state lighting applications due to their advantages over conventional white LEDs such as ultra-low costs, low heating temperature, mechanical flexibility and large photoactive areas when produced with wet processing methods. This paper discusses development of such VLC links with a view to implementing ubiquitous broadcasting networks featuring advanced modulation formats such as orthogonal frequency division multiplexing (OFDM) or carrier-less amplitude and phase modulation (CAP) in conjunction with equalization techniques. Finally, this paper will also summarize the results of the European project ICT COST IC1101 OPTICWISE (Optical Wireless Communications - An Emerging Technology) dealing VLC and OLEDs towards 5G networks.

ACWSN: an adaptive cross layer framework for video transmission over wireless sensor networks

Wireless multimedia sensor networks (WMSNs), have limited resources in terms of computational, memory, bandwidth, and battery capability, which makes transmitting multimedia content over it, is a challenge as multimedia requires QoS guarantee. Recently adopting cross-layer design in WMSNs proved to be a promising approach, which improves quality of service of WSN under various operational conditions. In this work, an adaptive cross layer framework for transmitting multimedia content over WSN (ACWSN) is presented, it is based on an extensive study of Group Of Picture structure effect on quality of multimedia transmission in various wireless channel states that is executed at sink node. It adaptably selects optimum video encoding parameters at application layer according to current wireless channel state which is communicated from physical layer and recommendations communicated from sink node; in addition an AVQ (adaptive video queue) which schedule packets according to its type to drop less important packets in case of network congestion. Simulation results show that ACWSN optimizes video quality in different wireless channel conditions.

Opportunistic Channel Scheduling for Ad Hoc Networks with Queue Stability

AbstractIn this paper, a distributed opportunistic channel access strategy in ad hoc network is proposed. We consider the multiple sources contend for the transmission opportunity, the winner source decides to transmit or restart contention based on the current channel condition. Owing to real data assumption at all links, the decision still needs to consider the stability of the queues. We formulate the channel opportunistic scheduling as a constrained optimization problem which maximizes the system average throughput with the constraints that the queues of all links are stable. The proposed optimization model is solved by Lyapunov stability in queueing theory. The successive channel access problem is decoupled into single optimal stopping problem at every frame and solved with

An Accelerometer-Assisted Power Management for Wearable Sensor Systems

In wearable sensor systems (WSSs), sensor nodes are deployed around human body parts such as the arms, the legs, the stomach, and the back. These sensors have limited lifetimes because they are battery-operated. Thus, transmission power control (TPC) is needed to save the energy of sensor nodes. The TPC should control the transmission power level (TPL) of sensor nodes based on current channel conditions. However, previous TPC algorithms did not precisely estimate the channel conditions. Therefore, we propose a new TPC algorithm that uses an accelerometer to directly measure the current channel condition. Based on the directly measured channel condition, the proposed algorithm adaptively adjusts the transmission interval of control packets for updating TPL. The proposed algorithm is efficient because the power consumption of the accelerometer is much lower than that of control packet transmissions. To evaluate the effectiveness of our approach, we implemented the proposed algorithm in real sensor devices and compared its performance against diverse TPC algorithms. Through the experimental results, we proved that the proposed TPC algorithm outperformed other TPC algorithms in all channel environments.

Distributed load aware relay selection algorithm for cooperative relay networks

Cooperative relaying is accepted as a promising solution to achieve high data rates over large areas in the 4G wireless system. This paper presents a two-step distributed load aware relay selection algorithm LA-RS for relay-based cooperative networks. According to current user channel conditions as well as the user numbers that relay serves, LA-RS chooses the optimal relay node for each user in a distributed way. More specifically, in the first step each mobile station MS constructs relay selection functions for candidate relay node RN, and selects the appropriate RN accordingly. Furthermore, in the second step RNs also adopt a weighted channel dependent scheduling algorithm for resource allocation, so as to provide a flexible tradeoff between per-user fairness and aggregate throughput in each cell. Simulation results demonstrate that compared with other relay selection schemes, LA-RS achieves load balancing through effective relay selection method, so as to obtain a tradeoff between the system throughput and the user equity.

Energy-Aware and Adaptive Cross Layer Framework for Video Transmission over Wireless Sensor Networks

Wireless Multimedia Sensor Networks (WMSNs), is a network of sensors which are limited in terms of computational, memory, bandwidth, and battery capability. Multimedia transmission over WSN requires certain Qos guarantees such as huge amount of bandwidth, strict delay and lower loss ratio, which makes transmitting multimedia content over it, is a challenging problem. Recently adopting cross-layer design in WMSNs proved to be a promising approach, which improves quality of service of WSN under various operational conditions. In this work, an energy aware framework for transmitting multimedia content over WSN (ECWMSN) is presented, where packet and path scheduling were introduced, so that It adaptably selects optimum video encoding parameters at application layer according to current wireless channel state, and schedules packets according to its type to drop less important packets in case of network congestion. Finally, path scheduling is introduced so that different packets types/priority is routed through suitable path with suitable Qos taking into consideration the network lifetime. Simulation results show that ECWMSN optimizes video quality and prolongs network lifetime.

Adaptive Long-Range Prediction of Three-State LMS Channel Model

In order to provide the accurate real-time knowledge of future channel state information for the adaptive transmission of narrowband land mobile satellite (LMS) communication systems, an adaptive long-range prediction (ALRP) method, suitable for a three-state LMS channel model at S-band, is proposed. The very slow shadowing conditions' variations of satellite propagation channel can be described as a three-state Gilbert---Elliot channel model based on Markov chain. The channel state of future long-range is predicted based on weighting prediction while the parameters of linear auto-regression model are updated using an iterative adaptive tracking algorithm. The future channel fading series are predicted by the latest observations within current channel state. Simulation results show that the proposed method can be used to predict the future long-range channel state and fading series of three-state Gilbert---Elliot channel model accurately; and it is observed from the mean square error results that the prediction performance of the ALRP method is much more accurate than that of long-range prediction method. Moreover, the method has advantage of real-time and low-complexity which will make the adaptive transmission techniques feasible for LMS channel models.

Cooperative relaying in user-centric networking under interference conditions

An ever-growing demand for pervasive Internet access has boosted the deployment of wireless local networks in recent decades. Nevertheless, wireless technologies face performance limitations due to unstable propagation conditions and mobility of devices. In face of multi-path propagation and low-data-rate stations, cooperative relaying promises gains in performance and reliability. However, cooperation procedures are unstable, due to their dependence on current channel conditions, and introduce overhead that can endanger performance, especially when nodes are mobile. This article presents an introduction to cooperative relaying, and describes a novel link layer protocol, called RelaySpot, able to implement cooperative relaying in dynamic networks, based on opportunistic relay selection, cooperative relay scheduling, and switching.

Outage Analysis of Multi-Antenna Rate Adaptive Systems With Outdated Feedback

The effect of imperfect channel state information (CSI) on rate adaptation in time-varying multi-antenna fading channels is studied. In the presence of feedback delay and channel estimation error, we analyze the outage probability (OP), defined as the average probability that the achievable rate in the current channel state is lower than data rate scheduled based on outdated feedback, for maximum ratio combining receivers in single-input multiple-output channels and zero-forcing (ZF) receivers in multiple-input multiple-output (MIMO) channels. In particular, for temporally correlated MIMO channels, the conditional distribution of SNR at the output of ZF detection in the current channel state is unknown; hence we apply a Gaussian approximation to obtain a closed-form expression for the average OP of the MIMO-ZF receiver. Simulation results show that our derivations are well-matched to the actual OP and throughput of multi-antenna rate adaptive systems. Also, based on our analysis results, we propose a simple rate adaptation scheme that maximizes the average throughput under a target OP constraint. The proposed schemes optimize the scheduled rate according to a given CSI condition, and effectively maximize the average outage-constrained throughput.

Hybrid Transmission Power Control for Wireless Body Sensor Systems

In wireless body sensor network systems (WB-SNSs), the sensor nodes have very limited battery power because they are tiny, lightweight, and wearable or implantable. As a result, WB-SNSs require a very efficient transmission power control (TPC) algorithm for effectively reducing energy consumption and extending the lifetime of sensor nodes. To achieve this goal, we propose a novel TPC algorithm referred to as hybrid TPC. The hybrid TPC algorithm adaptively selects a conservative or an aggressive control mechanism depending on current channel conditions. The conservative control mechanism, which slowly changes transmission power level (TPL), is suitable in a dynamic environment. On the other hand, the aggressive control mechanism, which rapidly changes TPL, is ideal in a static environment. In order to evaluate the effectiveness of the hybrid TPC algorithm, we implemented various TPC algorithms and compared their performances against the hybrid TPC algorithm in different channel environments. The experimental results showed that the hybrid TPC algorithm outperformed other TPC algorithms in all channel environments.

Variable-Rate Transmission for MIMO Time-Correlated Channels With Limited Feedback

In this paper we consider variable-rate transmission for time-correlated MIMO (multi-input multi-output) channels with limited feedback. The number of bits loaded on each subchannel of the MIMO system is dynamically assigned according to the current channel condition and fed back to the transmitter. As the channel is time-correlated, bit loading is a vector signal that is also time-correlated. We propose to feedback bit loading using predictive coding, which is known to be a powerful quantization technique when the underlying signal is correlated in time. Assuming the channel is a first-order Gauss-Markov random process, we derive the predictor for the bit loading to be coded and analyze the corresponding prediction error variance when the channel is varying slowly. By exploiting the prediction error variance, we adapt the quantizer of the prediction error to have a smaller quantization error. Furthermore we show that the prediction error variance is proportional to a term that depends only on the time-correlation coefficient. This leads to the conclusion that, a codebook that is designed for a particular time correlation coefficient can be easily modified to a codebook for a different correlation coefficient without redesign. Simulations are presented to demonstrate that the proposed predictive coding can achieve a very good approximation of the desired transmission rate with a very low feedback rate.

위성통신 시스템에서 이동형 위성단말을 위한 개루프 전력제어 알고리즘

ABSTRACT In this paper, we propose an open loop power control algorithm to control transmission power of the On-The-Move(OTM) Satcom terminal in GEO satellite communication environment. The proposed algorithm identifies the current channel state restricted by an obstacle or an antenna depointing loss based on the received beacon signal strength. On the basis of the determined signal attenuation causes, the OTM Satcom terminal turns off the RF output when an antenna tracking is failed. If the OTM Satcom terminal experiences a channel blockage by an obstacle, the terminal spreads the transmit data to increase data reception probability. To evaluate the performance of the proposed algorithm, we compare an adjacent satellite interference level and an outage probability. The results show the performance of the proposed algorithm is better than that of the conventional algorithm. 키워드 : 위성통신, 이동형 위성단말, 전력제어, 위성통신채널, 대역확산 Key word : Satellite communications, OTM terminal, Power control, Satellite communication channel, Spread spectrumJournal of the Korea Institute of Information andCommunication Engineering

Adjusting Control Packet Transmission Intervals in Low Power Sensor Systems

In order to construct an efficient wireless sensor system, it is necessary to increase the lifetime of its battery-operated sensor nodes. To this end, a wireless body sensor system adopts a transmission power control (TPC) mechanism. However, existing TPC mechanisms adjust the transmission power level (TPL) according to the received signal strength indication (RSSI) value of the most recently received data packet. Therefore, they do not effectively cope with dynamically changing wireless body channel environments. In particular, when a wireless channel is unstable, changes in the TPL should be avoided to prevent energy consumption due to unnecessary transmission and reception of control packets. Accordingly, this paper proposes a new TPC mechanism that adaptively changes the control packet transmission interval on the basis of the current channel condition. Further, actual sensors are used to experimentally verify that the proposed mechanism (1) performs well in all channel environments and (2) facilitates the construction of an efficient wireless body sensor system.

재난방송용 대기모드 해제신호 검출을 위한 최적 부호 성능 분석

최근 전 세계적으로 지진, 쓰나미와 같이 막대한 인명과 재산 피해를 야기시키는 자연재난이 증가함에 따라 재난에 효과적으로 대응하기 위한 방송 시스템에 대한 요구가 증가하고 있다. 재난 방송시스템에서는 재난 발생 시 재난정보를 보다 빠르고 효과적으로 전달하기 위하여, 단말을 깨워 재난 방송 채널로 자동 변환 시켜주는 대기모드해제(wake-up) 신호가 사용된다. 본 논문에서는, 재난 방송시스템을 위한 대기모드해제 검출 방법을 제안한다. 재난방송용 대기모드 해제신호는 기존 디지털TV 시스템과의 간섭을 줄이기 위하여 저전력/협대역에서 고려되어야 하며, 좋은 자기 상관 특성을 가져야한다. 우선, 본 논문에서의 자기상관특성이 우수한 단일 m-시퀀스와 상보부호(complementary code)를 이용한 대기모드해제의 적합성을 분석하고, 신호 대 잡음비에 따른 성능을 검증한다. 다음으로 대기모드 해제신호의 검출 성능을 향상시키기 위하여, 의사잡음 계열의 Barker 부호 및 Walsh-Hadamard 부호를 이용한 직접확산 방식의 신호 전송 포맷을 제안한다. 제안된 직접확산방식에 의한 대기모드 해제신호 검출 방법은 확산 이득으로 인하여 단일 m-시퀀스와 Golay 부호(이진 상보부호)를 이용한 방법보다 뛰어난 검출 성능을 나타낸다. Recently, the need for disaster-preventing broadcast has increased gradually to cope with natural disaster like earthquake and tsunami causing enormous losses of both life and property. In disaster-preventing broadcast system, the wake-up signal is used to alert user terminal and switch the current state of channel to the emergency channel, which is for the fast and efficient delivery of emergency information. In this paper, we propose the detection method of wake-up signal for disaster-preventing broadcast systems. The wake-up signals for disaster-preventing broadcast should have a good auto-correlation property in low power and narrow-band conditions that does not affect the existing digital television (DTV) system. The suitability of the m-sequence and complementary code (CC) is analyzed for wake-up signals according to signal to noise ratio. A wake-up signal is proposed by combining the direct sequence spread spectrum (DSSS) technique and pseudo noise (PN) sequences such as Barker and Walsh-Hadamard codes. By using the proposed method, a higher detecting performance can be achieved by the spreading gain compared to the single long m-sequence and the Golay code.

IFrag: interference-aware frame fragmentation scheme for wireless sensor networks

Reliable data transmission is a fundamental challenge in resource-constrained wireless sensor networks. In current implementations, a single bit error requires retransmitting the entire frame. This incurs extra processing overhead and power consumption, especially for large frames. Frame fragmentation into small blocks with individual error detection codes can reduce the unnecessary retransmission of the correctly received blocks. The optimal block size, however, varies based on the wireless channel conditions. In this paper, we propose an interference-aware frame fragmentation scheme called iFrag. iFrag dynamically adjusts the number of blocks inside a frame based on current channel conditions, and effectively addresses all challenges associated with such dynamic partitioning. Through analytical and experimental results, we show that iFrag achieves up to $$3\times$$ improvement in goodput when the channel is noisy, while reducing the delay by 12 % compared to other static fragmentation approaches. On average, it shows a 13 % gain in goodput across all channel conditions used in our experiments. Our testbed results also show that iFrag lowers the energy consumed per useful bit by 60 %, as improved data transmission reliability reduces the number of frame retransmissions which increases the motes energy efficiency.

Adaptive Traffic-Aware PSM Mechanism for IEEE 802.11 WLANs

AbstractWireless devices consume large amounts of energy during wireless communication. As the energy storage of battery is limited, improving energy efficiency has become an important approach to prolong the lifetime of devices. The IEEE 802.11 protocol supports the power save mode (PSM) in wireless local area networks (WLANs). However, the standard PSM cannot adapt to the changes of traffic load or channel conditions. Therefore, this article proposes an adaptive traffic-aware PSM mechanism (APSM) that improves energy efficiency of wireless devices in a WLAN with an access point (AP). According to the current channel condition and traffic load, the AP adjusts the interval of beacons that give devices different priorities to fetch buffered packets. The devices can adaptively adjust listening intervals according to network traffic, and adopt different congestion backoff timers when channel collisions happen or the network topology changes. The APSM has been implemented and evaluated in NS-2. The simulation results have shown that devices using the APSM can improve energy efficiency by 115% at most compared with the ones using the standard PSM. The benefit of adaptive beacon interval and listening intervals is significant, while the improvement due to the adaptive backoff timer is minor. The improvement of the APSM over the PSM is more significant when the network traffic level decreases and the ratio of idle power to sleeping power increases. Additionally, the APSM increases the delay of data frames within a limited range, which does not bring any bad effect on network throughput.

Recent human impacts and change in dynamics and morphology of ephemeral rivers

Abstract. Ephemeral streams induce flash-flood events, which cause dramatic morphological changes and impacts on population, mainly because they are intermittent and less predictable. Human pressures on the basin modify load and discharge relationships, inducing dormant instability on the fluvial system that will manifest abruptly during flood events. The flash-flood response of two ephemeral streams affected by load supply modification due to land use changes is discussed in a combination of geomorphic and hydraulic approaches. During the Rivillas flash flood, intensive clearing on the basin led to high rates of sediment flowing into an artificially straightened and inefficient channel. The stream evolved from a sinuous single channel into a shallow braiding occupying the entire width of the valley floor. Misfits and unsteady channel conditions increased velocity, stream power and sediment entrainment capacity and considerably magnified flood damage. Resulting morphosedimentary features revealed a close relationship with the valley floor post-flood hydraulic model, and pre-event awareness would have made it possible to predict risk-sensitive areas. In the second case, the Azohía stream, modelling of current pre-flood channel conditions make it possible to determine channel narrowing and entrenchment in the lower alluvial fan stretch. Abandonment of intensive agriculture, basin reforestation and urbanization diminish load contribution and trigger channel incision. This induces an increase in slope and velocity in the bankfull channel, producing renewed erosive energy and thus activating upstream propagation of incision and bank undermining. The absence of water-spreading dynamics on the alluvial fan in favour of confinement in a single channel produces an unstable dynamic in the system, also offering a false sense of stability, as long as no large magnitude floods occur. When modelling flood-prone areas and analysing hydraulic variables, it is important to detect possible anthropic disturbances that may affect basin load budgets in order to anticipate catastrophic consequences resulting from inappropriate fluvial management before the occurrence of an extraordinary event.

Impact of Feedback Channel Delay over Joint User Scheduling Scheme and Separated Random User Scheduling Scheme in LTE-A System with Carrier Aggregation

In Long Term Evolution-Advanced (LTE-A), the signal quality in a wireless channel is estimated based on the channel quality measurements. The measurement results are used to select suitable modulation and coding scheme for each transmission, feedback, and processing delay, which can cause a mismatch between channel quality information (CQI) and current channel state at the base station. However, prospect delays in the reception of such CQI may lead to a system performance degradation. This study analyzes the impact of CQI feedback delay on joint user scheduling (JUS) scheme and separated random user scheduling (SRUS) scheme in LTE-A system over carrier aggregation. The analysis will be compared with the system having delayed channel and perfect knowledge at different deployment scenario. We will study the throughput performance of both scheduling schemes with different deployment scenario, and then recommend the suitable deployment scenario to keep the desired QoS for a specific number of users. Results show that, in main beam directed at sector boundaries and diverse coverage, JUS scheme performs better than SRUS, which can justify the intensive use of user equipment power and extra control signaling overhead.

Multi-User Pre-Processing in Multi-Antenna OFDM TDD Systems with Non-Reciprocal Transceivers

The combination of OFDM with joint pre-processing in adaptive multi-antenna systems offers both an ease of equalization in frequency-selective channels and keeping the signal processing at the mobile stations simple. In addition, the spatial dimension can be efficiently exploited to ensure high system throughput. With the utilization of higher-order modulation the performance of the system is highly sensitive to multiple access interference and nonorthogonal subchannels due to hardware impairments or insufficient adaptation to the current channel conditions. A further source of error in TDD systems are the non-reciprocal transceivers inhibiting the baseband-to-baseband channel reciprocity required for accurate channel state acquisition based on the uplink channel estimate. In this paper, measurement results of a low-cost hardware-based calibration are presented and the drawbacks are discussed leading to the utilization of a recently introduced relative calibration. The latter is applied to an OFDM system and achieves or at least approximates the baseband-to-baseband reciprocity. Thus, it enables the link adaptation using the uplink channel state information. Furthermore, preliminary hardware implementations of the relative calibration running on a real-time system show accurate results.