Rate-adaptive System Research Articles

Capsule endoscopy for small-intestinal disorders: Current status.

Small-bowel capsule endoscopy (SBCE) is used widely because of its non-invasive and patient-friendly nature. SBCE can visualize entire small-intestinal mucosa and facilitate detection of small-intestinal abnormalities. In this review article, we focus on the current status of SBCE. Several platforms for SBCE are available worldwide. Third-generation SBCE (PillCam® SB3) has a high-resolution camera equipped with an adaptive frame rate system. Several software modes have been developed to reduce the reading time for capsule endoscopy and to minimize the possibility of missing lesions. The main complication of SBCE is capsule retention. Thus, the main contraindication for SBCE is known or suspected gastrointestinal obstruction unless intestinal patency is proven. Possible indications for SBCE are obscure gastrointestinal bleeding, Crohn's disease, small-intestinal polyps and tumors, and celiac disease. Colon capsule endoscopy (CCE) can observe inflamed colonic mucosa non-invasively, and allows for the continuous and non-invasive observation of the entire intestinal tract (pan-endoscopy). Recently, application of CCEas pan-enteric endoscopy for inflammatory bowel diseases (including Crohn's disease) has been reported. In the near future, reading for CE will be assisted by artificial intelligence, and reading CE videos for long periods will not be required.

A Hybrid Data Compression Scheme for Power Reduction in Wireless Sensors for IoT.

This paper presents a novel data compression and transmission scheme for power reduction in Internet-of-Things (IoT) enabled wireless sensors. In the proposed scheme, data is compressed with both lossy and lossless techniques, so as to enable hybrid transmission mode, support adaptive data rate selection and save power in wireless transmission. Applying the method to electrocardiogram (ECG), the data is first compressed using a lossy compression technique with a high compression ratio (CR). The residual error between the original data and the decompressed lossy data is preserved using entropy coding, enabling a lossless restoration of the original data when required. Average CR of 2.1 × and 7.8 × were achieved for lossless and lossy compression respectively with MIT/BIH database. The power reduction is demonstrated using a Bluetooth transceiver and is found to be reduced to 18% for lossy and 53% for lossless transmission respectively. Options for hybrid transmission mode, adaptive rate selection and system level power reduction make the proposed scheme attractive for IoT wireless sensors in healthcare applications.

Interplay Between Optimal Selection Scheme, Selection Criterion, and Discrete Rate Adaptation in Opportunistic Wireless Systems

An opportunistic, rate-adaptive system exploits multi-user diversity by selecting the best node, which has the highest channel power gain, and adapting the data rate to selected node's channel gain. Since channel knowledge is local to a node, we propose using a distributed, low-feedback timer backoff scheme to select the best node. It uses a mapping that maps the channel gain, or, in general, a real-valued metric, to a timer value. The mapping is such that timers of nodes with higher metrics expire earlier. Our goal is to maximize the system throughput when rate adaptation is discrete, as is the case in practice. To improve throughput, we use a pragmatic selection policy, in which even a node other than the best node can be selected. We derive several novel, insightful results about the optimal mapping and develop an algorithm to compute it. These results bring out the inter-relationship between the discrete rate adaptation rule, optimal mapping, and selection policy. We also extensively benchmark the performance of the optimal mapping with several timer and opportunistic multiple access schemes considered in the literature, and demonstrate that the developed scheme is effective in many regimes of interest.

RED theory for quality of service provisioning in wireless communications

In this paper, we study the performance limit of a wireless communication system over a fading channel. The system under study consists of 1) a finite-buffer discrete-time queueing system on the link layer; and 2) a rate-adaptive channel coding system on the physical layer. The objective of this paper is to analyze the relationship among data rate (R), packet error probability (E), and delay bound (D) under the interaction between the link layer and the physical layer. In our analysis, we consider three types of packet errors; that is, 1) packet drop due to full buffer; 2) packet drop due to delay bound violation; and 3) packet decoding error due to channel noise. We obtain an upper bound on the packet error probability. Furthermore, by minimizing the packet error probability over the transmission rate, we obtain an optimal rate control policy that guarantees the user-specified data rate and delay bound. In the case of constant arrival, the optimal rate control policy results in a rate-error-delay triplet; then, by varying data rate and delay bound, we obtain rate-error-delay Pareto-optimal surface, which serves as the performance limit of the system under study. Copyright © 2012 John Wiley & Sons, Ltd.

Adaptive Demodulation in Differentially Coherent Phase Systems: Design and Performance Analysis

Adaptive Demodulation (ADM) is a newly proposed rate-adaptive system which operates without requiring Channel State Information (CSI) at the transmitter (unlike adaptive modulation) by using adaptive decision region boundaries at the receiver and encoding the data with a rateless code. This paper addresses the design and performance of an ADM scheme for two common differentially coherent schemes: M-DPSK (M-ary Differential Phase Shift Keying) and M-DAPSK (M-ary Differential Amplitude and Phase Shift Keying) operating over AWGN and Rayleigh fading channels. The optimal method for determining the most reliable bits for a given differential detection scheme is presented. In addition, simple (near-optimal) implementations are provided for recovering the most reliable bits from a received pair of differentially encoded symbols for systems using 16-DPSK and 16- DAPSK. The new receivers offer the advantages of a rate-adaptive system, without requiring CSI at the transmitter and a coherent phase reference at the receiver. Bit error analysis for the ADM system in both cases is presented along with numerical results of the spectral efficiency for the rate-adaptive systems operating over a Rayleigh fading channel.

Power Control for Adaptive Rate Wireless Networks

In this paper, we study the power control for the adaptive rate system that adapts the data rate to the channel and interference condition by adjusting the SINR requirement. The power control technique aims to decrease the interference to obtain the satisfactory throughput. We first find the optimal CINR that allows as many users as possible to transmit their data with the satisfied throughput requirements. Then we use the optimal CINR as the target CINR in the proposed distributed power control algorithm. During the operation of this algorithm, we let each user adjust the transmit power for several iterations to obtain the satisfactory CINR, which in turn leads to the satisfactory throughput. We show that the user can meet its throughput requirement by increasing the number of iterations, and once the user meets its throughput requirement, this condition will hold from then on. Furthermore, it is proven that the throughput can converge to the throughput requirement for each user.

The COGNITION Study Rationale and Design: Influence of Closed Loop Stimulation on Cognitive Performance in Pacemaker Patients

Several studies showed the beneficial effect of pacemaker implantation on cognitive performance in patients with bradycardia. But it has never been investigated if patients with chronotropic incompetence may improve their cognitive performance if treated by a rate-adaptive system reacting to mental stress in comparison to the most frequently used accelerometer-driven pacing. The randomized, single-blind, multicenter COGNITION study evaluates if closed loop stimulation (CLS) offers incremental benefit in the speed of cognitive performance and the overall well-being of elderly patients with bradycardia compared with accelerometer-based pacing. Four hundred chronotropically incompetent patients older than 55 years will be randomized 3-6 weeks after implantation to CLS or accelerometer sensor. Follow-up visits are performed after 12 and 24 months. The speed of cognitive performance, which is the underlying function influencing all other aspects of cognitive performance, will be assessed by the number connection test, a standardized psychometric test for the elderly. Secondary endpoints include patient self-assessment of different aspects of health (by visual analogue scales), quality of life (by SF-8 health survey), the incidence of atrial fibrillation (episodes lasting for longer than 24 hours), and the frequency of serious adverse events. In the ongoing COGNITION study, we aim at long-term comparison of two rate-adaptive systems, focusing on the cognitive performance of the patients, which was neglected in the past evaluation of pacemaker sensors.

On Analysis and Design of Low Density Generator Matrix Codes for Continuous Phase Modulation

We investigate the analysis and design of low density generator matrix (LDGM) codes for continuous phase modulation (CPM). The system uses LDGM codes as an outer code for CPM. For additive white Gaussian noise channels, we derive the union bound to analyze the error floor performance. Design principles for lowering error floors are suggested from this analysis. We propose a design approach of jointly considering the LDGM code degree and the CPM modulation index. Then we consider the rate-adaptive system for slowly fading channels. By changing the rate of the LDGM codes, the information rate of the CPM signals is adapted according to channel variations. We use a low-rate LDGM code as the mother code. Higher rates are achieved by puncturing the output of these codes. To exploit the rate-flexible property of punctured LDGM codes, a rate function is proposed to calculate the rate of each transmitted block. Thus, we can have a quasi-continuous information rate. Numerical results show that this approach can improve the energy efficiency from a discrete-rate adaptation. Using the rate-adaptive approach, up to 11 dB transmitted energy gain can be achieved from the non-adaptive scheme in the low bit-error-rate region (smaller than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) for minimum shift keying (MSK).

Distributed adaptive rate system for wireless packet networks

A distributed adaptive rate system for wireless packet networks is proposed. Compared to the centralized adaptive rate system that needs to know the packet retransmission probability to maximize the throughput, this system need not know the packet retransmission probability in advance and can achieve the optimal adaptive rate system that maximizes the throughput for wireless packet networks.

Adaptive demodulation using rateless erasure codes

We introduce a rate-adaptive system in which the receiver demodulates only those bits that have a high probability of being correct, treating nondemodulated bits as erasures. Several sets of decision regions, derived using composite hypothesis testing, are proposed for 16-QAM and 16-phase-shift keying, which allow for the simple implementation of this demodulation strategy. We demonstrate that pre-encoding the data with a Raptor code allows for simple reconstruction of the message, regardless of the erasure pattern introduced from the nondemodulated bits. We prove the optimality of the proposed decision regions in selecting the most likely subset of bits from any received symbol in moderate-to-high signal-to-noise ratios, and we analyze the performance of demodulating with these decision regions over an additive white Gaussian noise channel. Also demonstrated is the strong performance of 16-QAM for this application, compared with other power-efficient constellations and the near-optimality of using Gray mapping, even under the proposed alternate sets of decision regions

Adaptive Rate System for Wireless Packet Networks

The severe channel and interference condition can limit the throughput of the wireless packet networks. We thus propose an adaptive rate system to increase the throughput of the wireless packet networks. In this system, the data rate is adapted to the channel and interference condition. By optimizing the data rate for a given channel and interference condition, we establish the optimal adaptive rate system. It can be shown that the optimal adaptive rate system provides higher throughput than the fixed rate system.

System Throughput Analysis of Rate Adaptive TDMA System Supporting Two Class Services

In this paper, an adaptive transmission scheme is proposed to improve the spectral efficiency of TDMA systems. Services accommodated in such systems are classified as QoS services and BE services. Unlike conventional adaptive TDMA systems where the time slot duration is fixed for each user, our proposed system employs transmission slots with adaptive duration. For QoS services, rate adaptive modulation is adopted to make use of the instantaneous channel conditions of individual user. For BE services, a media access control strategy (MAC) that takes the instantaneous transmission conditions of all physical links of all BE services into consideration is employed. A tramework to study the proposed system in terms of the average packet loss and the average system throughput is presented. The maximum nuumber of QoS services that can be supported in the system while a predefined requirement on the average packet loss is still satisfied is investigated. A comparison study shows that our proposed scheme has higher system throughput over both conventional fixed and adaptive TDMA systems.

Throughput–delay performance of interference level-adaptive transmission in voice∕data integrated CDMA network with variable spreading gain

The throughput and delay performance of adaptive spreading gain uplink packet transmission in real-time and non-real-time data integrated CDMA networks are analysed under AWGN and Rayleigh fading channels. The processing gain for the non-real-time data is adaptively changed according to the total uplink interference level so that a required signal-to-interference ratio (SIR) can be achieved. The optimum values for the required SIR with regard to maximising the throughput are derived as a function of packet length. The optimised adaptive rate system achieves significantly improved throughput compared to the non-adaptive rate system. In addition, the adaptive rate system achieves almost linear increase in packet delay with traffic density, while the packet delay of the non-adaptive rate system shows an abrupt increase as traffic density increases.

Long-Term Experience with a Contractility (Autonomic Nervous System) Driven Pacemaker Sensor in Patients with Chronic Chagasic Cardiomyopathy

We analyzed performance of a ventricle-paced, ventricle-sensed, inhibited, rate-responsive (VVIR) pacemaker driven by autonomic nervous system activity sensor in chagasic patients with cardiac conduction system disturbances. Forty-seven chagasic patients were studied (28 male, 19 female; age, 24-68 years). Thirty-six patients had complete atrioventricular (AV) block, eight had second-degree AV block, and the remaining three patients had sinus node disease. Patients were divided into two groups according to their heart rate (HR) at rest: group 1 had an HR more than 65 bpm; group 2, HR less than 65 bpm. A comparative study that extended over the first 12 months after pacemaker implantation evaluated: HR at rest and during various types of stress tests, arterial blood pressure at rest and during exercise, and performance of the TIR-60 UP leads in conjunction with the sensor function as compared with the performance of other leads. Patients from group 1 had a higher HR at rest and a smaller HR variation during stress test than did patients from group 2. This indicates that with this type of rate-adaptive system it is possible to control each patient individually. The blood pressure at rest and during stress tests did not differ between the two patient groups. With respect to the sensor function, the TIR-60 UP leads offered the same performance as others leads. The VVIR pacemaker equipped with the sensor of autonomic nervous system activity allowed chagasic patients to restore their physiologic mechanisms. Seventy-four percent of the patients had the New York Heart Association Functional Class improved by 1 or 2 steps, after the pacemaker implantation.

Adaptive processing gain CDMA networks over Poisson traffic channel

The performance of an adaptive data rate transmission for uplink code-division multiple-access (CDMA) networks is analyzed where the processing gain is adaptively changed according to the channel traffic density in order that a desired signal-to-interference ratio (SIR) can be achieved. The throughput of the adaptive rate system is asymptotically constant with respect to the proposed traffic density and is significantly improved compared to the fixed rate system. In addition, as the traffic density increases the adaptive rate system achieves almost linear increase in the channel delay, while that of the fixed rate system shows abrupt increase.

Packet Transmission over a Fixed Wireless Loop Using Adaptive Rate Techniques

In this paper a rate-adaptive transmission scheme is used to ensure reliable and efficient transmission of packets over a fixed wireless link. The scheme is based on a stationary, memoryless, and blockfading channel model with perfect knowledge of channel fading state, available at transmitters. Information, in our proposed system, is transmitted in the form of packets that each may potentially consist of several conventional ATM cells along with a rate-identifier preamble that contains the information needed by a receiver, allowing for proper demodulation/decoding of packets. In this application, because of the short physical length of a radio link, a simple go-back-N ARQ protocol can provide a reliable communications system with an acceptable throughput. Analytical results for spectral efficiency, throughput and queuing delay show that adaptive-rate systems can achieve significant improvements over those using fixed-rate schemes.

Safety of a permanent unipolar rate adaptive pacemaker during prolonged helicopter travel

Environmental interference with implanted rhythm management devices may result in inappropriate pacemaker inhibition and bradycardia or inappropriate stimulation and tachycardia. In permanent rate adaptive pacemakers with motion-based activity sensors or unipolar electrodes, this interference may be particularly problematic. We report the first case of repeated, prolonged exposure of a unipolar, motion-based rate adaptive pacemaker system in a pacemaker-dependent patient without sequelae.

Analysis of an adaptive rate convolutionally coded multicarrier DS/CDMA system

The analysis of an adaptive rate convolutionally coded multicarrier direct sequence code division multiple-access (DS/CDMA) system is considered. In order to accommodate a number of coding rates easily and make the encoder and decoder structure simple, we use the rate-compatible punctured convolutional (RCPC) code. We obtain data throughputs at several coding rates, and choose the coding rate that has the highest data throughput in the signal-to-interference and noise ratio (SINR) sense. To achieve maximum data throughput, a rate adaptive system is proposed based on the channel state information (the SINR estimate). The SINR estimate is obtained by the soft decision Viterbi decoding metric. We show that the proposed rate adaptive convolutionally coded multicarrier DS/CDMA system can enhance the spectral efficiency and provide frequency diversity.

Survey of cardiac pacing and implanted defibrillator practice patterns in the United States in 1997.

A survey of implanters of permanent cardiac pacemakers and ICDs in the United States during 1997 was conducted to identify present and changing patterns in indications for pacing, implantation techniques, pacing-mode selection, follow-up, and opinions regarding pacing and ICD related issues. This report is an update from 1993 of surveys performed every 4 years for the International Cardiac Pacing and Electrophysiology Society (ICPES). Questionnaires were sent to implanting physicians who were members of the North American Society of Pacing and Electrophysiology (NASPE), and who might, therefore, be expected to be more conversant than others with the state of the art. Four major manufacturers also provided estimates of the numbers of pacemakers and ICDs implanted in the United States from 1994 through 1997. In 1997, approximately 182,000 new rhythm management devices, including 153,000 primary pacing systems and 29,000 ICDs, were implanted, an increase of 24% for pacemakers and 90% for ICDs since 1994. In 1997, pacemaker implantations were performed by about 8,600 physicians working in 3,300 hospitals and 1,000 independent "surgi-centers." From 1994 to 1997, sales in the United States of dual chamber pacemakers rose from 58% to 69% of the total, and adaptive rate systems from 74% to 90%. ICD sales increased by about 29% per year from 18,700 to 35,000 units. This study disclosed significant differences among implanter subcategories and between present and earlier practices, and it provided useful insights into trends in pacemaker and defibrillator practice. Future surveys would be facilitated if a standardized implant registry like that used in Europe were established in the United States.

Performance of an adaptive rate modem using quasi-analytic simulation techniques

The symbol error probability (SEP) of a digital signal processor implemented /spl pi//M M-ary differentially coherent phase-shift keying (MDPSK) modem, using quasi-analytical (QA) simulation techniques, is the subject of this investigation. We study M values of 4, 8, 16, 32, and 64 for use in a fast adaptive data rate mobile radio communication system. The proposed modulation scheme /spl pi//M-MDPSK, is a generalization of /spl pi//4 differentially coherent quadrature phase-shift keying, which is used in the North American time-division multiple-access wireless standard. A QA simulation approach is developed so that real system impairments can be studied without having to resort to lengthy Monte Carlo simulation. In particular, it is found that implementation losses, most notable at M=32 and 64, which result from practical transmit and receive filtering, and symbol timing error, can be largely overcome by using a fixed equalization filter and increased accuracy of symbol timing recovery. We focus on an additive white Gaussian noise channel since, in a fast adaptive rate system, the Doppler spread mobile channel is approximately Gaussian on short time intervals. However, the quasi-analytic technique developed here is directly extendable to a fast Rayleigh fading channel. Specifically, we find that for M=64, the inclusion of a fixed seven-tap zero forcing equalizer at the matched filter output, decreases the SEP degradation at P/sub e/=10/sup -4/ from 7.5 dB down to 0.24 dB. The symbol timing error using a finite-precision interpolator is held to within 1/64 symbol period.