Adaptive power control for wireless communication systems with time-varying delay

In this paper, adaptive control is proposed for hybrid position/force synchronization of master-slave teleoperation systems with time-varying delays in communication channels. Different from previous works on bilateral teleoperation systems, we investigate position/force control of bilateral teleoperation systems subject to time-varying delays and dynamical uncertainties. Using partial feedback linearization, the dynamics of both master and slave are transformed into two subsystems: local master/slave position/force control with unmodeled dynamics and delayed position/force synchronization. An adaptive control is proposed to deal with the dynamical uncertainties and robust against time delays, which guarantees the position/force synchronization trajectories converge to the desired manifolds with prescribed performance. The stability of the closed-loop system and the boundedness of synchronization tracking errors are proved using linear matrix inequalities based on Lyapunov stability synthesis. The position/force tracking error up to an ultimately bounded error is achieved. The proposed adaptive controls are robust against relative motion disturbances, parametric uncertainties, and time delays, and are validated by experimental studies.

The load changes of working machinery in the running process will certainly result in poor matches in the characteristics of the transmission system. For the issue, this paper studies the adaptive power control model and algorithm. The adaptive power control system is developed using the adaptive power control technology based on the load identification, and is applied in the full AC electric forklift and the CNC band sawing machine. The variable frequency system and intelligent control method based on the integration of the load characteristic recognition and control proposed in this paper, adaptively adjust the parameters of the PID controller according to the load characteristic parameters identified real-timely for the transmission system of the working machinery, so as to achieve the best performance matches, the highest effectiveness and lowest energy consumption of the entire transmission system.

This paper proposes a joint adaptive rate selection and power control algorithm for broadband TDMA/TDM wireless networks. The proposed algorithm is a modified, enhanced, and more robust version of the selective power control with active link protection (SPC-ALP) algorithm proposed for adaptive transmission rate and power control in CDMA networks [R.Jantti and S. Kim, 2000]. Unlike SPC-ALP, the proposed algorithm uses adaptive coding and modulation (instead of variable spreading gain) for transmission rate control. In addition, the proposed algorithm is different in two aspects; the first one is the inclusion of the cochannel interferer assistance mode, while the second one is the use of the signal quality as a criterion for user removal. Results show that the proposed algorithm outperforms SPC-ALP in terms of the net throughput and signal quality measures such as the outage probability and frame error rate. Channel reallocation is also studied and found to be very effective in enhancing the system performance particularly at low to medium loading.

An enhanced adaptive scheme based on threshold method with a reduced complexity that combine adaptive modulation and coding with diversity combining is presented for throughput maximization in broadband code division multiple access (CDMA) satellite networks. The proposed algorithm is a modify, enhanced, and more robust version of the existing algorithms for adaptive transmission rate and modulation in CDMA networks. The rate compatible punctured turbo-coded (RCPT), which has been found to give improved throughput performance in a direct sequence (DS) CDMA is exploited. A semi-analytical process and simulations were carried out. It is found that there are significant improvement in the average throughput and the bit-error performance. The proposed algorithm using adaptive coding and modulation (instead of variable spreading gain) outperforms other systems such as Selective Power Control with Active Link Protection (SPC-ALP) algorithm proposed for adaptive transmission rate and power control in CDMA networks.

In this paper we developed a framework for resource allocation in multi-class traffic CDMA system using adaptive power control and antenna array multiuser receiver. We devised a new scheme in which both transmit power and receiver filter adapt to the time-varying channel state. An antenna array multiuser receiver that jointly processes received signal vectors from multiple antennas and maximizes the signal-to-interference ratio for each user is proposed. It is combined with adaptive power control based on target SIR for each user. Our scheme can support multi-class traffic with different SIR requirements and guarantee their quality of service in multipath fading environment. A theoretical bound is derived to characterize capacity of CDMA system using adaptive power control and antenna array multiuser receiver in multipath fading environment. Simulations show that actual system capacity in multipath finding environment is close to the theoretical bound at large power constraint. Capacity at various power constraints can be characterized by a notion of bandwidth utility. It is also demonstrated that the antenna array multiuser receiver is quite effective in increasing capacity of users with higher SIR requirement and lower power constraint.

Code-division multiple-access (CDMA) is a serious candidate for personal communication systems at 1.9 GHz in North America. We consider the issue of bandwidth management in a CDMA integrated wireless-access network with heterogeneous services. A framework for adaptive connection admission in the up-link direction is proposed. It is based on estimation of the interference at the base station receivers. The estimation algorithm employs a linear Kalman filter which is driven by a measurement of the interference and by predicted traffic parameters of the admitted connections. We derived several generic variants of the control architecture for the up-link direction to assess the main characteristics of the framework and to determine the trade-offs between complexity and performance. They vary from a fixed strategy with fixed power control to an adaptive strategy with full information about network state and adaptive power control. A numerical study of the proposed framework shows that the estimated value of the average interference adapts well to the real value under nonstationary and nonuniform environment. This feature results in high network utilization for arbitrary traffic conditions.

In this paper, adaptive controls are proposed for hybrid motion/force synchronization of master-slave tele-operation system with unsymmetric time-varying delays in communication channels. Using partial feedback linearization, the whole tele-operation system contained both master and slave manipulator dynamics is transformed into two subsystems: local master/slave motion/force control with unmodelled dynamics and delayed motion/force synchronization. Then, adaptive controls combing Linear Matrix Inequalities (LMIs) are proposed to deal with the dynamical uncertainties and robust against time delay. The proposed controls are robust against relative motion disturbances, parametric uncertainties and time delays, which are validated by extensive simulation studies.

Markovian jumping systems have arisen naturally in the mathematical modeling of phenomena spanning disciplines in the social sciences, natural sciences, and engineering. This kind of stochastic dynamical systems can be employed to model the dynamics when parameters are subject to random abrupt changes due to sudden environment changes, subsystem switching, system noises, executor faults, and so forth. Much attention has been given to modeling, optimization, and real applications of such stochastic dynamical systems in the literature in recent years. As the advanced control and optimization will provide a basis for the design and application of such stochastic systems, these advanced techniques would result in substantial and sustainable benefits. The accepted papers in this special issue include stochastic stability, stabilization, stochastic control optimization, system modeling and identification methods, predictive control, signal processing, robust filtering, multiagent systems, networked control systems, time-delayed systems, neural networks, the Takagi-Sugeno fuzzy systems, simulated annealing, and fault detection methods.

Radio frequency spectrum in wireless communication is a common resource shared by all collocated devices. Most spectrum management schemes rely on a centralized base station-receiver station relaying architecture. In contrast, infrastructure-less systems including wireless ad hoc networks require a scalable, distributed methodology. Moreover, the access has to be coordinated among the nodes in the network in the aspects which include power and rate adaptation. The challenge is to find an optimal tradeoff between such parameters not only for a particular link but also for an entire multi-hop network. Several existing schemes address power, throughput and Signal-to-Interference ratio (SIR) control on a link level. In contrast, the proposed work performs optimization for the entire network. The game theory methodology is employed to solve the distribution of the radio resources while the adaptive power and rate control estimates the required but unknown radio interface parameters online. Moreover, the adaptive power and rate control scheme optimizes the local channel access. The resulting spectrum channel management scheme becomes a hybrid of adaptive controls and game theory approaches that guarantees a fair and efficient channel sharing and maximizes the overall performance. The results are shown analytically and through simulations.

A digital cellular radio code-division multiple-access (CDMA) system can only support a finite number of users before the interference plus noise power density, I/sub 0/, received at the cellular base station causes an unacceptable frame-error rate. Once the maximum interference level is reached, new arrivals should be blocked. In a power-controlled CDMA system, the base station can direct mobiles to reduce their power and data rate to reduce interference and allow more users on the system. This approach is employed in TIA IS-95 with respect to the time-varying voice activity on cellular voice channels. We investigate an alternative technique where we adjust the power and data rate of mobile data users to the time-varying interference level to allow more users on a congested system. This scheme was simulated for various proportions of voice and data users and offered traffic levels. Blocking probabilities are reduced in some cases by two orders of magnitude. Message wait time, now a random variable, may exceed the wait time for a constant rate system at high traffic levels. If the cellular carrier has a maximum blocking requirement, an adaptive rate/power system can increase the capacity. For example, a base station that normally supports 26.4 Erlangs offered traffic with 2% blocking can support 33.5 Erlangs with the same blocking probability if adaptive rates and power control are used. Thus, the adaptive rate system can increase the capacity by 27%.

Information broadcasting technique from vehicles to vehicles under emergency situation aiming adaptive cruise control is researched in this paper. At the transmitter, code division multiple access (CDMA) based intensity modulation to visible light beam is used, while at the receiver, a matched filter after direct detection is employed to recover the signal. Our simulation results indicate that for one thing, CDMA technique can help the system to realize broadcasting characteristic. When there is no CDMA, the system cannot work, while when CDMA is employed, the system can get a bit error rate (BER) performance of 10-3. For another, CDMA can also help to resist the background noise. With the aid of CDMA technique, the system can get of BER of 10-3 even in very heavy background noise. The system design can benefit the vehicle adaptive cruise control, especially under some emergency situation.

In this paper the application of an adaptive reference-free feedback controller to a nonlinear aeroelastic system subjected to steady aerodynamic loads is examined. The numerical simulations show that when using the angle-of-attack as a feedback signal, the system chaotic motion and LCOs can be suppressed by properly selecting the adaptive filter cut-off frequency and the feedback gain. In addition the controller is augmented with a time delay parameter; it has been determined that it is possible to obtain the regions of instability due to time delay in a nonlinear aeroelastic system under adaptive closed loop control.

We report a rigorous approach to analyze the effects of nonlinear distortion on code division multiple access (CDMA) wireless communication systems based on time-domain analysis and band-pass nonlinearity theory. Given AM-AM and AM-PM characteristics of a nonlinear device, this technique is capable of predicting adjacent channel power rejection (ACPR), noise power ratio (NPR), two-tone intermodulation products, CDMA waveform quality, and baseband signal vector constellation at the output of the nonlinear device. To demonstrate and verify the capability of this technique, an L-band power amplifier was designed, built, tested with CDMA waveforms, and compared with the simulated results. Excellent agreement between the measured and predicted results has been achieved.

In this paper, a novel adaptive inverse power control method that is based on the filtered-x LMS (FxLMS) algorithm is introduced. Inverse power control minimizes the interference that a cognitive radio creates to licensed users and allows more users to share the spectrum. It is also needed in multi-access systems like code division multiple access (CDMA) to alleviate the near-far problem. The proposed variable step algorithm adjusts the step size in a nearly optimal way. Based on numerical analysis this new method clearly improves system performance compared to the algorithm where the well-known fixed or variable step adjustment power control is used. A normalized version of the FxLMS algorithm is needed in a fading channel. In a slowly fading channel (e.g., normalized Doppler frequency of 0.001) the FxLMS power control can keep the received signal-to-noise ratio (SNR) in the desired level with a good accuracy most of the time. The standard deviation of the received SNR is 1.92 dB when the received SNR is kept at 10 dB. The results with almost all different SNR values are better than the other methods can achieve.

This paper is concerned with the problem of designing output feedback controller and guaranteed cost controller of discrete-time singular piecewise-affine systems with time delay and norm-bounded time-varying parameters uncertainties. Firstly, the corresponding operating region of the time-delay singular piecewise-affine systems in state space is described as ellipsoid which can be solved by a set of vector inequalities. Then, based on a singular piecewise Lyapunov-Krasovskii function combined with S-procedure and some matrix inequality convexifying techniques, the output feedback controller of the time-delay singular systems is investigated, and meanwhile, the guaranteed cost controller of the time-delay singular piecewise-affine systems is solved in terms of linear matrix inequalities (LMIs). It is shown that the controller gains can be obtained by solving a family of LMIs parameterized by one or two scalar variables. Numerical examples are given to illustrate the effectiveness of the proposed design methods. Moreover, it is suitable for practical application.