Adaptive error control for reliable systems-on-chip

This paper presents an adaptive rate error control scheme for digital communication over time-varying channels. The cyclic code with majority-logic decoding is used in a cascaded way as an inner code to create a simple and powerful hybrid-ARQ error control scheme. Inner code is used only for error correction and the outer code is used for both error correction and error detection. When an error is detected, retransmission is required. The unsuccessful packets are not discarded as with conventional schemes, but are combined with their retransmitted copies. Approximations for the throughput efficiency and the undetectable error probability are given. A high reliability coupled with a simple high-speed implementation makes it suitable for high data rate error control over both stationary and non-stationary channels. Adaptive error control scheme becomes the best solution for time-varying channels when the optimum code is selected according to the actual channel conditions to enhance the system performance. The main feature of this system is that the basic structure of the encoder and decoder need not be modified while the error-correction capability of the code increases. Results of a comparative analysis show that the proposed scheme outperforms other similar ARQ protocols. >

In Reference 1, a class of extraction formulations were developed to recover solution quantities with superconvergent accuracy. As a continuation, this paper documents some new developments in the boundary stress extraction method to expand its applications to boundary locations that are not traction‐free. Furthermore, the convergence characteristics of the extracted pointwise stress are investigated in an h‐adaptive process using different adaptive error control schemes. Observations from those numerical experiments provide some initial insight toward the development of an adaptive approach that can obtain prescribed pointwise solution accuracy with optimal computation efficiency.

We evaluate the performance of an adaptive error correction scheme for wireless ATM networks (WATM). This scheme attempts to minimize the system throughput in order to satisfy the user defined quality of service (QoS) constraints. Indeed, error control for high speed wireless ATM networks is an important research topic, even wireless communication channels are highly affected by unpredictable factors like co-channel interference, adjacent channel interference, propagation path loss and multipath fading. We propose an intelligent-agent architecture to implement our mechanism A-BCH-FEC (adaptive BCH FEC scheme) for a Rayleigh fading environment. Intelligent agents are distributed over all system entities. In the latter, base station agents cooperate with other agents to choose the appropriate BCH coding scheme related to a specific level of signal-to-noise-ratio (SNR). Finally, we illustrate our implementation by some simulation results from a cellular system. These results show that the adaptive scheme using BCH codes improves significantly the system performance.

Automatic repeat request (ARQ) has been widely used for its high reliability and convenience in implementation. But its low performance is shown when the channel is in a noisy state. This paper presents an adaptive error control scheme with combination of FEC and ARQ. An encoder and a decoder for large constraint length convolution codes are constructed by TMS320E25 microprocessors to implement error control. Based on channel condition, the system can modify the diffuse convolution codes constraint length automatically. Such an adaptive error control system combined with an ARQ system based on HDLC protocol is efficient to transmit data at high speed using bad radio channels.

In this paper we focus on the adaptive control of structural acoustics using intelligent structures with embedded piezoelectric (PZT) patches and low cost digital signal processor systems. After a discussion on the adaptive feedforward control scheme, a hybrid adaptive control scheme is proposed, which takes advantage of both feedback control and adaptive feedforward control. The two schemes are realized on a low-cost, small volume, convenient and universal digital signal processing (DSP) board. A carbon fiber reinforced polymer plate with two embedded PZT patches is developed and used in two experiments. The first experiment is adaptive interior noise control using the intelligent plate, in which the adaptive feedforward control scheme is employed. Obvious noise reduction is obtained for constant frequency, swept frequency and varying amplitude harmonic disturbances. The second experiment is adaptive control of sound-induced vibration of the plate, where two embedded PZT patches are used as an actuator and a sensor, respectively, and the hybrid adaptive controller is applied. The full vibration reduction for various harmonic excitations is obtained, verifying the advantage of the hybrid adaptive control. It is demonstrated that active control of structural acoustics can be efficiently achieved by employing intelligent structures, advanced adaptive control schemes and the low-cost DSP board.

The advisability of using adaptive strategies in channels with side information at the transmitter is considered. Different adaptive strategies are defined for block codes (BC) and punctured convolutional codes (PCC) and compared on throughput and bit error probability after decoding.

Exploiting the adaptive properties of a probing device for TCP in heterogenous networks

Wireless links are known to suffer location-dependent, time-varying, and bursty errors. This paper considers a class of adaptive error-control schemes in the data link layer for reliable communication over wireless links in which the error-control code and the frame length are chosen adaptively, based on the estimated channel state/condition. Three error-control schemes are considered according to: (1) the number of Reed Solomon code segments a packet is divided into and (2) the way a lost packet is retransmitted. Through throughput performance and computation complexity analyses, these three schemes are compared, and then one of them is claimed to be the most attractive in terms of computation complexity and practicality even though its throughput performance is not the best. The simulation results also verify that this scheme works well over a time-varying fading channel. Error control for the medium access control (MAC) header and its effect on the performance of each error-control scheme are also considered since, without proper error protection for the header, it would be futile to exercise error control on the user data.

Presents an adaptive error control technique based on the use of type-I hybrid-ARQ protocols. The communication channel is assumed to be slowly varying and is modeled using a finite state Markov chain. The system counts the number of retransmission requests during an observation interval called a frame and, together with knowledge of the error control strategy in use and a set of thresholds, estimates the state of the channel. The coding strategy which maximizes throughput while maintaining a minimum required level of reliability is chosen for use in the next frame. Examples are provided showing system design and performance using families of Reed-Solomon codes. >

Communication in high-speed wireless local area networks such as IEEE 802.11a are known to suffer from location-dependent, time-varying, and burst errors. It is usual to implement forward error correction and automatic repeat request mechanisms in the physical and data link layer to combat this errors. In this paper we evaluate the system performance of a WLAN with the CSMA/MAC protocol with different ARQ protocols. We have implemented three different schemes: (1) selective repeat ARQ; (2) ARQ with majority voting; and (3) type II hybrid ARQ. The simulation results show that all three schemes perform well when the channel is in good condition but when the bit error rate (BER) increases the type II hybrid ARQ is superior to the other two schemes.

Recently, a class of adaptive control schemes called L1 Adaptive Control (L1-AC) has been proposed and widely advertised in aerospace control for achieving fast and robust adaptation and better performance than the existing Model Reference Adaptive Control (MRAC) Schemes. The L1-AC scheme is designed mainly for plants with full state measurement even though the name L1-AC has been used as an umbrella name for more general classes of plants. In this paper, we show that the L1-AC for plants with measured states is simply a standard MRAC with a low pass filter inserted in front of the control input. The analysis of the scheme is almost identical to that of MRAC as the same Lyapunov function is used to establish stability. The motivation for using the filter is the fact that for this class of adaptive schemes i.e. MRAC for plants with full state measurement the tracking error can be made arbitrarily small during transient by increasing the adaptive gain. A high adaptive gain however makes the differential equation of the adaptive law or estimator very stiff and leads to numerical problems that cause high oscillations in the estimated parameters leading to loss of adaptivity and deviations from what the theoretical properties dictate. The L1-AC approach mistook these numerical oscillations as properties of the adaptive scheme and inserted an input low pass filter in order to filter them out. While the filter helps reduce the frequency of these oscillations in the control law the price paid is high. First the numerical instability does not go away and the estimated parameters continue to oscillate without converging to the true parameters even in the presence of sufficiently rich signals. Second, due to the filter the tracking error is no longer guaranteed to converge to zero and the transient bounds for the tracking error also depend on the filter. As a result, the tracking properties of the L1-AC scheme are worse than what a simple MRAC scheme can generate with adaptive gains that could be high but away from the region of numerical instability. In addition, the presence of the filter reduces the robust stability margins in the presence of unmodeled dynamics and provides literally no advantage as simple robust MRAC techniques can solve the same problem achieving much better properties. The authors of L1-AC often compare the properties of a numerically unstable MRAC due to extremely high adaptive gains something that is prohibited by robust adaptive control with those of the filtered MRAC aka L1-AC to show that L1-AC performs better. Such comparisons are not only misleading but do not reveal what causes what giving the reader a false impression of a new theory that results to new performance and robustness improvements. The use of filters in adaptive control is not new and they are used to improve the performance and robustness of certain adaptive control schemes without destroying their ideal tracking properties. In this paper we present such a scheme that guarantees good transient performance and robustness and reveals the trade off between transient performance and robust stability.

Data-driven model based adaptive feedback-feed forward control schemes for open cycle - OTEC process

This paper investigates the feasibility of adaptive control scheme for vibration suppression of flexible beam. The dynamic model of the flexible cantilever beam using finite element modeling is derived. Adaptive vibration controllers are good candidates for problems where parameters of a plant are unknown or there are uncertainties in a system. Parameters of adaptive controllers are adjusted on-line to achieve the best performance. Two adaptive vibration control schemes: adaptive feedforward control scheme using least mean square algorithm and model reference adaptive control algorithm are developed to suppress the vibration. Computer simulations are performed to verify the effectiveness of the proposed adaptive vibration control schemes and demonstrate their applications in vibration control.

The throughput performance of a broadcast DS/SSMA packet radio network using adaptive error control is investigated. Simulated results for the network throughput against offered load are presented and show that adaptive error control significantly increases the throughput performance at all offered loads.

The paper proposes an error control scheme that dynamically adjusts the polling schedule so that more corrupted messages can be manipulated within their deadlines for real-time communication on IEEE 802.11 wireless LAN. Monitoring the current traffic in the CFP (collision free period) interval as well as inspecting whether a node is executing an error control procedure, the AP (access point) terminates CFP, if possible, to extend the duration of the next CP (collision period). With the enlarged time, the AP gives more polls to the node in need to increase the number of timely recovered messages. Simulation result performed via SMPL shows that this adaptation scheme can reduce the message discard due to transmission error by 5.5%, compared with the existing error controls method for real-time communication on WLAN.