Adaptive Coding Scheme Research Articles

Mitigating MAC Layer Performance Anomaly of Wi-Fi Networks through Adaptable Channelization

802.11 wireless local area networks (WLANs) can support multiple data rates at physical layer by using adaptive modulation and coding (AMC) scheme. However, this differential data rate capability introduces a serious performance anomaly in WLANs. In a network comprising of several nodes with varying transmission rates, nodes with lower data rate (slow nodes) degrade the throughput of nodes with higher transmission rates (fast nodes). The primary source of this anomaly is the channel access mechanism of WLANs which ensures long term equal channel access probability to all nodes irrespective of their transmission rates. In this work, we investigate the use of adaptable width channelization to minimize the effect of this absurdity in performance. It has been observed that surplus channel-width due to lower transmission rate of slow nodes can be assigned to fast nodes connected to other access points (APs) which can substantially increase the overall throughput of the whole network. We propose a medium access control (MAC) layer independent anomaly prevention (MIAP) algorithm that assigns channel-width to nodes connected with different APs based on their transmission rate. We have modeled the effect of adaptable channelization and provide lower and upper bounds for throughput in various network scenarios. Our empirical results indicate a possible increase in network throughput by more than 20% on employing the proposed MIAP algorithm.

Mitigating MAC Layer Performance Anomaly of Wi-Fi Networks through Adaptable Channelization

802.11 wireless local area networks (WLANs) can support multiple data rates at physical layer by using adaptive modulation and coding (AMC) scheme. However, this differential data rate capability introduces a serious performance anomaly in WLANs. In a network comprising of several nodes with varying transmission rates, nodes with lower data rate (slow nodes) degrade the throughput of nodes with higher transmission rates (fast nodes). The primary source of this anomaly is the channel access mechanism of WLANs which ensures long term equal channel access probability to all nodes irrespective of their transmission rates. In this work, we investigate the use of adaptable width channelization to minimize the effect of this absurdity in performance. It has been observed that surplus channel-width due to lower transmission rate of slow nodes can be assigned to fast nodes connected to other access points (APs) which can substantially increase the overall throughput of the whole network. We propose a medium access control (MAC) layer independent anomaly prevention (MIAP) algorithm that assigns channel-width to nodes connected with different APs based on their transmission rate. We have modeled the effect of adaptable channelization and provide lower and upper bounds for throughput in various network scenarios. Our empirical results indicate a possible increase in network throughput by more than 20% on employing the proposed MIAP algorithm.

Adaptive Modulation and Coding Using Neural Network Based SNR Estimation

In this paper, we propose a novel Adaptive Modulation and Coding (AMC) scheme enabled by Artificial Neural Network (ANN) aided Signal-to-Noise power Ratio (SNR) estimation. The Power Spectral Density (PSD) values are trained for SNR classification and it is mapped to respective Modulation and Coding Scheme (MCS) sets. Once trained, optimal MCS can be determined in low calculation complexity. The proposed approach is robust especially in high mobility environment since the PSD appearance is hardly influenced by the Doppler shift. Its effectiveness in terms of throughput is presented through computer simulations compared to the existing Error Vector Magnitude (EVM) based link adaptation scheme.

A cross-layer analysis of TCP/link adaptation technologies over free-space optical links with Markov error model

This paper presents a comprehensive cross-layer framework on the performance of transmission control protocol (TCP) over a free-space optical (FSO) link, which employs automatic repeat request (ARQ) and adaptive modulation and coding (AMC) schemes. Not similar to conventional works in the literature of FSO, we conduct a Markov error model to accurately capture effects of burst errors caused by atmospheric turbulence on cross-layer operations. From the framework, we quantify the impacts of different parameters/settings of ARQ, AMC, and the FSO link on TCP throughput performance. We also discuss several optimization aspects for TCP performance.

Regularized Zero-Forcing Precoding-Aided Adaptive Coding and Modulation for Large-Scale Antenna Array-Based Air-to-Air Communications

We propose a regularized zero-forcing transmit precoding (RZF-TPC)-aided and distance-based adaptive coding and modulation (ACM) scheme to support aeronautical communication applications, by exploiting the high spectral efficiency of the large-scale antenna arrays and link adaption. Our RZF-TPC-aided and distance-based ACM scheme switches its mode according to the distance between the communicating aircraft. We derive the closed-form asymptotic signal-to-interference-plus-noise ratio (SINR) expression of the RZF-TPC for the aeronautical channel, which is Rician, relying on a non-centered channel matrix that is dominated by the deterministic line-of-sight component. The effects of both realistic channel estimation errors and of the co-channel interference are considered in the derivation of this approximate closed-form SINR formula. Furthermore, we derive the analytical expression of the optimal regularization parameter that minimizes the mean square detection error. The achievable throughput expression based on our asymptotic approximate SINR formula is then utilized as the design metric for the proposed RZF-TPC-aided and distance-based ACM scheme. Monte-Carlo simulation results are presented for validating our theoretical analysis as well as for investigating the impact of the key system parameters. The simulation results closely match the theoretical results. In the specific example that two communicating aircrafts fly at a typical cruising speed of 920km/h, heading in opposite direction over the distance up to 740km taking a period of about 24 min, the RZF-TPC-aided and distance-based ACM is capable of transmitting a total of 77 GB of data with the aid of 64 transmit antennas and four receive antennas, which is significantly higher than that of our previous eigen-beamforming transmit precoding-aided and distance-based ACM benchmark.

A hybrid encoding method for reducing code stream in EICA-optimized SMVQ reversible data hiding

An enhanced imperialist competitive algorithm (EICA)-optimized side-match vector quantization (SMVQ)-based reversible data hiding (VQ-SMVQ with EICA) was developed for embedding higher number of secret bits. This technique improved the embedding capacity rate of compression and quality of reconstruction. However, for improving security and minimizing the length of the output code stream left-upper coding (LUC) was along with SMVQ, since LUC algorithm is more appropriate for compression of SMVQ index table. In this paper, the code stream size is reduced by proposing an efficient encoding approach. Initially an improved locally adaptive coding (ILA) scheme is used for effective distribution of the position of SMVQ indices based on adaptive threshold value. A locally adaptive data compression scheme (LAS) is utilized with IAS to improve the compression rate of secret data simultaneously with embedding capacity. The combined technique is achieved highly reduced length of output code stream. Thus, EICA-optimized SMVQ reversible data hiding with hybridized ILA and LAS outperforms than existing schemes.

Adaptive Modulation and Coding with Selective Retransmission under OFDM signaling

In this paper, we present bandwidth efficient selective retransmission method in conjunction with adaptive modulation and coding (AMC) scheme for OFDM waveform. In the proposed method, when a packet failure occurs, receiver requests retransmission of information symbols prone to error corresponding to the low signal-to-noise ratio (SNR) sub-carriers of OFDM modulation. The selective retransmission avoids unnecessary retransmission and AMC chooses a proper modulation and coding scheme with an objective to maximize the throughput. Our method achieves higher throughput as compared to conventional retransmission methods such as Chase combining hybrid automatic repeat reQuest (CC-HARQ) and incremental redundancy hybrid automatic repeat reQuest (IR-HARQ). We also provide the throughput and delay analysis of the proposed method for non-truncated ARQ. The simulation results demonstrate throughput gain without significant impact on delay as compared to the conventional retransmission approaches.

Runtime Techniques to Mitigate Soft Errors in Network-on-Chip (NoC) Architectures

As aggressive scaling continues to push multiprocessor system-on-chips (MPSoCs) to new limits, complex hardware structures combined with stringent area and power constraints will continue to diminish reliability. Waning reliability in integrated circuits will increase the susceptibility of transient and permanent faults. There is an urgent demand for adaptive error correction coding (ECC) schemes in network-on-chips to provide fault tolerance and improve overall resiliency of MPSoC architectures. The goal of adaptive ECC schemes should be to maximize power savings when faults are infrequent and increase application speedup by boosting fault coverage when faults are frequent. In this paper, we propose runtime adaptive scrubbing (RAS), a novel multilayered error correction and detection scheme with three modes of operation enabled by an area-efficient configurable encoder for encoding packets on the switch-to-switch (s2s) layer, thus preventing faults from accumulating up the network stack and onto the end-to-end layer. As fault rates fluctuate we propose a dynamic methodology for improving fault localization and intelligently adapt fault coverage on demand to sustain graceful network degradation. RAS successfully improves network resiliency, fault localization, and fault coverage as compared to traditional static s2s schemes. Simulation results demonstrate that static RAS improves network speedup by 10% for Splash-2/PARSEC benchmarks on a $8 \times 8$ mesh network while reducing area overhead by 14% and incurring on an average 6.6% power penalty by boosting fault tolerance when fault rates increase. Further, our dynamic RAS scheme maintains 97.88% of network performance for real applications while incurring 20% power penalty.

Delay-tolerant distributed space-time coding with feedback for cooperative MIMO relaying systems

An adaptive delay-tolerant distributed space-time coding (DSTC) scheme equipped with a feedback channel is proposed for two-hop cooperative multiple-input multiple-output (MIMO) networks. A maximum likelihood receiver and adjustable code matrices subject to a power constraint with a decode-and-forward cooperation strategy are considered with different DSTC antenna configurations. In the proposed delay-tolerant DSTC schemes, an adjustable code matrix is employed to transform the space-time coded matrices at the relay nodes. Stochastic gradient and least squares algorithms are also developed with reduced computational complexity. The proposed algorithms are then extended to a cooperative MIMO system using amplify-and-forward strategy and opportunistic relaying algorithms in order to develop a delay-tolerant coding scheme combined with optimal relay selection strategies. An upper bound on the pairwise error probability and a rank criterion analysis are derived which indicate the advantage of the proposed algorithms. Simulation results show that the proposed algorithms obtain significant performance gains and address the delay issue in cooperative MIMO systems as compared to existing DSTC schemes.

Throughput Maximization by Adaptive Switching with Modulation Coding Scheme and Frequency Symbol Spreading

It is required to realize higher transmission rate and higher reliability for mobile communication due to the increase in Internet use. However, wireless channel capacity can not be used with maximum efficiency due to fluctuating channels affected by shadowing, multipath fading and mobility. Adaptive modulation and coding (AMC) scheme is now commonly implemented to maximize the throughput performance under the given link qualities. Forward Error Correction (FEC) based link adaptation is effective to improve throughput in a lower SNR regime, however, it immolates maximal throughput in good channel condition. Frequency symbol spreading (FSS) has been proposed that can improve BER even without FEC. It fully exploits the frequency diversity gain by spreading symbol per subcarrier to all frequency components. This paper proposes a new adaptation control scheme for OFDM by switching FSS and legacy AMC. Simulation result verifies its maximized throughput performance harvesting both of frequency diversity gain and coding gain.

Channel Capacity of High Altitude Platform Systems: A case study

This paper presents a model for Multiple-Input Multiple-Output (MIMO) Land High Altitude Platform channels and analytical evaluation of Discrete-input Continuousoutput Memoryless Channel capacity for High Altitude Platform (HAP)–MIMO systems, where practical transmission environments are considered. Furthermore, for HAP– Single-Input Single-Output (SISO) systems, we propose an adaptive transmission mechanism relying on the transmit power characterized by value at the transmitter side. Achievable channel capacity bounds are established for both idealized and realistic adaptive coding schemes with well-adopted modulation types, namely Phase Shift Keying and Quadrature Amplitude Modulation. DOI: 10.32913/rd-ict.vol3.no14.540

Analyzing the QoS Parameters in WiMAX Using Adaptive Modulation and Coding Schemes with HARQ

Analyzing the QoS Parameters in WiMAX Using Adaptive Modulation and Coding Schemes with HARQ

On the performance of adaptive coding schemes for energy efficient and reliable clustered wireless sensor networks

Clustering is the key for energy constrained wireless sensor networks (WSNs). Energy optimization and communication reliability are the most important consideration in designing efficient clustered WSN. In lossy environment, channel coding is mandatory to ensure reliable and efficient communication. This reliability is compromised by additional energy of coding and decoding in cluster heads. In this paper, we investigated the trade-off between reliability and energy efficiency and proposed adaptive FEC/FWD and FEC/ARQ coding frameworks for clustered WSNs. The proposed schemes consider channel condition and inter-node distance to decide the adequate channel coding usage. Simulation results show that both the proposed frameworks are energy efficient compared to ARQ schemes and FEC schemes, and suitable to prolong the clustered network lifespan as well as improve the reliability.

LTE-TDD 시스템에서 혼합 ARQ 응답을 이용한 적응적 변조 코딩 구성 선택 알고리즘

LTE-TDD 시스템에서 혼합 ARQ 응답을 이용한 적응적 변조 코딩 구성 선택 알고리즘

Three-Dimensional Adaptive Modulation and Coding for DDO-OFDM Transmission System

We propose a 3-D adaptive loading algorithm (ALA), which can individually allocate proper modulation formats, power levels, and the forward error correction codes to each orthogonal frequency division multiplexing (OFDM) subcarrier according to the estimated channel state information (CSI). The introduced look-up table operation can reduce the iterations and improve the convergence speed. To evaluate the performance of the proposed algorithm, we tailor the system parameters of direct detection optical OFDM (DDO-OFDM) to investigate the difference of effective data rate (EDR) between fixed schemes and proposed adaptive modulation and coding (AMC) schemes. When the fiber length is set to 90 km and received optical power (ROP) is −10 dBm in simulation, the AMC scheme achieves 7.86 Gb/s EDR, which is 1.93 times of the maximum EDR the fixed schemes can achieve under the bit error rate (BER) constraint. Compared with the Levin−Campello algorithm, the 3-D ALA improves about 3% and 6% data rates in poor and good CSI, respectively. In experiments, when the fiber length and ROP are 50 km and −18 dBm, respectively, the AMC scheme achieves the EDR of 4.96 Gb/s, which is 2.84 times of the maximum EDR of the fixed schemes under the BER constraint.

Channel Assembling Strategy in Cognitive Radio Networks: a Queuing Based Approach

With channel assembling strategies (CAS), more capacity and spectrum utilization can be achieved. However, blocking and forced termination occurs whenever the primary user (PU) arrives individually, or in batch. Motivated by a realistic scenario in cognitive radio networks, we proposed a joint CAS with queue (CAS+Q) which take into account the dynamics of a wireless link and other factors that affect the quality and capacity of the accessible channel. For CAS+Q to be practical, it must consider the time varying wireless link, a finite buffer regime, the traffic classes and adaptive modulation and coding (AMC) scheme. The introduction of a queuing regime for secondary users (SUs) is to ensure that traffic that would have been blocked or forcibly terminated would otherwise be queued in a buffer and possibly served later. This is to improve spectrum utilization and more especially, minimize blocking and forced termination of the SUs services. An investigation of the proposed strategy (CAS+Q) featuring AMC showed improved system performance when compared to our previous study without a queuing regime. It also showed the impact of delays on the proposed strategy depending on the system parameters selected. Extensive system simulations validate the analytical investigation.

On the design of coding framework for energy efficient and reliable multi-hop sensor networks

Energy efficiency and reliability are the key requirements for wireless sensor network (WSN), as sensor nodes are expected to be stand-alone for a long time and communication to be successfully carried out. Communication is the most energy consuming process in WSN, especially in lossy environment. In multi-hop WSN, packets are more susceptible to transmission errors which worsens the communication reliability and energy consumption. Therefore, coding schemes are mandatory to cover the channel impairments and save the transmission energy. In this work, we propose an adaptive coding (AC) scheme that can be adapted with the channel state and inter-node distances in order to decode and correct the packets or request for retransmissions. The proposed scheme has proved to be energy efficient and adaptive compared to Automatic Repeat reQuest (ARQ) and Forward Error Correction (FEC) schemes.

Adaptive modulation and coding techniques for global navigation satellite system inter‐satellite communication based on the channel condition

Inter-satellite link (ISL) will play an increasingly important role in the next generation of global navigation satellite system (GNSS). The inter-satellite distances in the GNSS vary greatly, resulting in a power loss difference of as much as 20 db. However, there are no reports on promotion of spectral efficiency in inter-satellite channels at present. In this study, the authors propose an efficient utilisation of the adaptive modulation and coding (AMC) scheme for ISLs in the GNSS. A novel method, based on inter-satellite distance, is presented for choosing the modulation and coding scheme (MCS). The proposed method provides a convenient way to estimate signal-to-noise ratio of the ISLs in GNSS. This AMC technique is implemented according to two different algorithms. One is the target bit error rate (BER) algorithm based on inter-satellite distance, aimed at keeping the BER below a target limit. The other is the maximum throughput algorithm based on inter-satellite distance, aimed at maximising the data throughput. In cases where the inter-satellite distance is short, simulation results show that, under the premise of the same transmission power, the throughput of two proposed AMC schemes is nearly six times that of a fixed MCS.

Scheduling for Video Transmission in LTE Downlink

Initial developments of cellular networks were intended for voice only applications. Later the need to support several applications and services lead to the evolution of mobile technology. In order to meet the growing user demands and high data rate requirements the fourth generation of mobile communication has adopted a standard called LTE. LTE provides high data rates, flexible bandwidth usage and low latency in networks. Scheduling is a feature employed at the eNodeB to allocate user equipments with available resources in the most efficient way. A scheduling scheme for video transmission is proposed in the downlink. A decision index is introduced in the algorithm which considers the status of the transmission queue and the quality of the channel connecting the eNodeB and the intended user equipment. Higher decision indexed valued user data is scheduled first. Index Terms: 4G, LTE, Video Codec, H.264, Resource Block, Channel Quality, CQI, Scheduling. I. Introduction Individuals exchange information between them through the process of communication. Communication can be done by any means such as gestures, vocabulary, written scripts and wired or wireless means. Nowadays wireless communication systems play a vital role in revolutionizing the means of information exchange. Mobile Communication categorically falls into the division of wireless communication. It is now one of the fastest means for conveying information between individuals. Mobile technology has evolved from the usage of analog devices to the digital counter parts. From first generation (1G) of mobile communication to the forthcoming fifth generation (5G) the difference in communication speed and bandwidth flexibility is clearly visible. Amplitude and frequency modulation techniques employed in the zeroth generation of mobile technology gave only a handful of channels for communication. Analog devices were designed for voice only applications in 1G which gave only low capacity voice channels. Later with digital techniques and multiple access schemes 2G provided unlimited access to limited channels. Wider range of applications such as voice telephony, video call, mobile TV, GPS (Global Positioning System) and video conferencing were supported by the third generation (3G) of mobile communications. However with the advent of newer technologies and a hike in user demands, the need for next generation of mobile technology became inevitable. Thus the evolution of fourth generation mobile technology occurred. 4G is clearly an improvement from its pre-existing technologies in terms of spectral efficiency, data rates and network capacity. LTE is the wireless standard adopted by the fourth generation of mobile technology. The adaptive modulation and coding (AMC) schemes, MIMO antenna technique and multicarrier modulation schemes such as OFDM jointly contributes to the high achievable data rates and spectral efficiency (3). In LTE systems, scheduling and resource allocation are the two important features adopted to ensure user satisfaction as well as efficient utilization of the available spectrum. Scheduling ensures the proper transmission and reception of the most urgent user data in the queue. Assignment of radio resources to users based on their quality of service (QoS) requirements and quality of the communication links is the main function of the scheduling and resource allocation processes.

Moore state machine for adaptive modulation and coding in high‐speed railway LTE‐R systems

An adaptive modulation and coding (AMC) scheme based on a Moore state machine is proposed for the high-speed railway communication systems. By setting a buffer zone for the signal-to-noise ratio threshold value, the proposed scheme is able to reduce the frequent transition of the modulation and coding scheme. Simulation results show that the proposed AMC strategy has a more stable spectral efficiency than the traditional AMC method using a piecewise function.