Provision of Guaranteed QoS with Hybrid Automatic Repeat Request in Interleave Division Multiple Access Systems

Provision of guaranteed quality of service (QoS) in wireless communication has always been a demanding task. QoS can be ensured by the mechanism of repeat request, however real time systems can tolerate only a finite delay. In this paper we investigate the problem of provision of guaranteed QoS by hybrid automatic repeat request (HARQ) schemes, based on soft outputs of a channel decoder. Focus is on adaptive interleavedivision multiple access (IDMA) transmission. Such a system is able to provide virtually arbitrary bit error rates (BER). The proposed HARQ schemes use the reliability information provided by the channel decoder to decide whether a packet satisfies the quality of service (QoS) requirements. QoS can be specified in terms of a minimum required throughput/data rate or a minimum required BER. Effect of truncation of repeat requests on the bit error rate and packet throughput is investigated. An adaptation scheme based upon the bit error rate in the accepted packets is proposed and the effect of the adaptation on the effective throughput is demonstrated

Energy and bursty packet loss tradeoff over fading channels: a system-level model

Energy efficiency and quality of service (QoS) guarantees are the key design goals for the 5G wireless communication systems. In this context, we discuss a multiuser scheduling scheme over fading channels for loss tolerant applications. The loss tolerance of the application is characterized in terms of different parameters that contribute to quality of experience (QoE) for the application. The mobile users are scheduled opportunistically such that a minimum QoS is guaranteed. We propose an opportunistic scheduling scheme and address the cross-layer design framework when channel state information (CSI) is not perfectly available at the transmitter and the receiver. We characterize the system energy as a function of different QoS and channel state estimation error parameters. The optimization problem is formulated using Markov chain framework and solved using stochastic optimization techniques. The results demonstrate that the parameters characterizing the packet loss are tightly coupled and relaxation of one parameter does not benefit the system much if the other constraints are tight. We evaluate the energy-performance tradeoff numerically and show the effect of channel uncertainty on the packet scheduler design

Energy-aware cooperative wireless networks with multiple cognitive users

In this paper, we study and analyze cooperative cognitive radio networks with arbitrary number of secondary users (SUs). Each SU is considered a prospective relay for the primary user (PU) besides having its own data transmission demand. We consider a multi-packet transmission framework that allows multiple SUs to transmit simultaneously because of dirty-paper coding. We propose power allocation and scheduling policies that optimize the throughput for both PU and SU with minimum energy expenditure. The performance of the system is evaluated in terms of throughput and delay under different opportunistic relay selection policies. Toward this objective, we present a mathematical framework for deriving stability conditions for all queues in the system. Consequently, the throughput of both primary and secondary links is quantified. Furthermore, a moment generating function approach is employed to derive a closed-form expression for the average delay encountered by the PU packets. Results reveal that we achieve better performance in terms of throughput and delay at lower energy cost as compared with equal power allocation schemes proposed earlier in the literature. Extensive simulations are conducted to validate our theoretical findings

Individual packet deadline delay constrained opportunistic scheduling for large multiuser systems

This work addresses opportunistic distributed multiuser scheduling in the presence of a fixed packet deadline delay constraint. A threshold-based scheduling scheme is proposed which uses the instantaneous channel gain and buffering time of the individual packets to schedule a group of users simultaneously in order to minimize the average system energy consumption while fulfilling the deadline delay constraint for every packet. The multiuser environment is modeled as a continuum of interference such that the optimization can be performed for each buffered packet separately by using a Markov chain where the states represent the waiting time of each buffered packet. We analyze the proposed scheme in the large user limit and demonstrate the delay-energy trade-off exhibited by the scheme. We show that the multiuser scheduling can be broken into a packet-based scheduling problem in the large user limit and the packet scheduling decisions are independent of the deadline delay distribution of the packets

Provision of Maximum Delay Guarantee at Low Energy in a Multi-user Environment

In this work a simple scheduling scheme is proposed for wireless sensor networks in presence of a maximum tolerable delay constraint. The scheduler performs the dual task of scheduling the users experiencing high channel gains to minimize the energy consumption while at the same time, it takes into account the maximum allowed buffer length of each user to provide an upper bound on the maximum tolerable delay. The idea of a threshold depending on the buffer occupancy is proposed to schedule the users opportunistically unless the deadline for transmission is reached. A maximum delay guarantee is provided in the proposed scheme in addition to average delay guarantee at almost no additional energy cost. The results show that multilevel recursive optimization can minimize energy subject to maximum bounded delay for schedulers that empty the buffer

Разработка генератора последовательностей цифровых импульсов: реферат дипломной работы / Писарик Ирина Владимировна; БГУ, Факультет радиофизики и компьютерных технологий, Кафедра информатики и компьютерных систем; науч. рук. Чудовский В. А.

In this study, the authors discuss relay selection schemes with the objective to minimise outage probability for a network consisting of a single source, multiple relays and a single destination. The relays are powered by radio frequency signals from the source. For a successful transmission, at least one of the relay nodes should be able to decode the source signals and have enough energy to relay the information to the destination. The authors assume that a relay node cannot decode information and harvest energy from the source signals simultaneously. The authors formulate an optimisation problem to minimise outage probability for the system. The relay selection scheme and the outage performance depend on the availability of the channel state information (CSI) on the source-relay and the relay-destination links. Based on the availability of the CSI on the relay-destination link, the authors propose relay selection schemes for different scenarios and evaluate the performance numerically. The results show that the availability of the CSI on the relay-destination link at the relay node helps to improve the outage performance considerably. The authors characterise the outage probability for the schemes analytically; and numerically compute the optimal number of relays which provide the optimal outage performance for a given scheme

Compact Full-Duplex Amplify-and-Forward Relay Design for 5G Applications

This paper presents a compact circuit design for implementing full-duplex relays serving network architectures envisioned for 5G applications. The proposed design prevents the transmit signal from interfering with the received signal through signal inversion. Signal inversion is accomplished through a compact design based on parametric amplifier circuit which operates simultaneously in two different modes, re-transmit and demodulate. This design also has an added advantage of being capable of generating phase difference between the transmitted and received signals by controlling the local oscillator signal. The validity of the design is evaluated against an example Smart Grid architecture, where it is employed to function as amplify-and-forward full-duplex relays/repeaters for serving several communication links. Simulation results indicate that full-duplex mode outperforms half-duplex one in terms of average channel capacity as well as bit error rate irrespective of the position of the relays with respect to distance from source/destination

ACADEMIC SUCCESS AND FAILURE AMONGST DENTAL STUDENTS: A MIXED METHODS STUDY OF WHAT MATTERS

OBJECTIVE: To explore various factors affecting academic success & failure among public sector dental students. METHODS: This mixed-methods study with explanatory sequential study approach was completed in May 2021 at Bolan Medical College, Quetta, Pakistan. After taking informed written consent, qualitative & quantitative questionnaires were distributed among 3rd year dental students. Quantitive data was analyzed through SPSS version-20. Qualitaive data was analysed through thematic analysis to identify themes and subthemes. RESULTS: Out of 28 dental students, majority (n=15; 53.6%) were females. Passing percentage of female students was high (n=14/15; 93.33%) as compared to males (n=7/13; 53.85%). Failure was 6.6% (n=1/15) in girls and 46.15% (n=6/13) in boys. In annual exams, 75% (n=21/28) students passed in all subjects. About 89.3% (n=25/28) of successful students were satisfied with teaching strategies, 85.7% (n=24/28) reflected on their learned material, 75% (n=21/28) recalled prior knowledge, 67.9% (n=19/28) were hard-working, 71.4% (n=20/28) were internaly motivated whereas 67.9% (n=19/28) were confident about their abilities. Instrumental design, personal issues and learning environment were the main themes identified. Sub-themes for instrumental design were teaching strategies, overload curriculum & exam strategies; for personal issues were learning style, lack of sleep, coping strategies, class attendance, stress & motivation/interest and for learning environment were students’ centered, assessment-centered and teachers’ centered. CONCLUSION: Successful students acknowledged the motivation, educational environment and innovative teaching strategies as contributing factors to their success. Hostel issues, lack of sleep, learning strategies, lack of interest in dentistry, anxiety, and parental education were the main elements among the academic failures