Dissertations / Theses on the topic 'Retransmission scheme'

Les demandes de haut débit, faible latence et grande fiabilité augmentent dans les nouvelles générations de systèmes de radiocommunications. Par conséquent, on propose de combiner la transmission non orthogonale avec les retransmissions HARQ afin de combattre les fluctuations de canal de transmission à haut débit. Dans la première partie de la thèse, on propose des protocoles de retransmissions HARQ avec l'aide d'un relai afin d'améliorer le débit et la fiabilité du système. Une version renforcée du protocole HARQ qui prend en compte le délai de retour est proposée dans la seconde partie de la thèse
HARQ has become an important research field in the wireless digital communications area during the last years. In this thesis, we improve the HARQ mechanisms in terms of throughput and/or latency which are the bottleneck of next generation wireless communication systems. More precisely, we improve the time-slotted HARQ systems by mimicking NOMA, which means using superposed packets in a single-user context. In the first part of the thesis, we propose HARQ protocols using the help of a relay to improve the transmission rate and reliability. An enhanced HARQ protocol adapted to delayed feedback is proposed in the second part. In this new multi-layer HARQ protocol, additional redundant packets are sent preemptively before receiving the acknowledgement, and in superposition to other HARQ processes

Les demandes de haut débit, faible latence et grande fiabilité augmentent dans les nouvelles générations de systèmes de radiocommunications. Par conséquent, on propose de combiner la transmission non orthogonale avec les retransmissions HARQ afin de combattre les fluctuations de canal de transmission à haut débit. Dans la première partie de la thèse, on propose des protocoles de retransmissions HARQ avec l'aide d'un relai afin d'améliorer le débit et la fiabilité du système. Une version renforcée du protocole HARQ qui prend en compte le délai de retour est proposée dans la seconde partie de la thèse
HARQ has become an important research field in the wireless digital communications area during the last years. In this thesis, we improve the HARQ mechanisms in terms of throughput and/or latency which are the bottleneck of next generation wireless communication systems. More precisely, we improve the time-slotted HARQ systems by mimicking NOMA, which means using superposed packets in a single-user context. In the first part of the thesis, we propose HARQ protocols using the help of a relay to improve the transmission rate and reliability. An enhanced HARQ protocol adapted to delayed feedback is proposed in the second part. In this new multi-layer HARQ protocol, additional redundant packets are sent preemptively before receiving the acknowledgement, and in superposition to other HARQ processes

Virginia Tech researchers have developed a broadband channel sounder that can measure channel quality while a wireless network is in operation. Channel measurements from the broadband sounder hold the promise of improving TCP/IP performance by trigging configuration changes in an adaptive data link layer protocol. We present an adaptive data link layer protocol that can use different levels of forward error correction (FEC) codes and link layer automatic retransmission request (ARQ) to improve network and transport layer performance.

Using a simulation model developed in OPNET, we determine the effects of different data link layer protocol configurations on TCP/IP throughput and end-to-end delay using a Rayleigh fading channel model. Switching to higher levels of FEC encoding improves TCP/IP throughput for high bit error rates, but increases end-to-end delay of TCP/IP segments. Overall TCP/IP connections with link layer ARQ showed approximately 150 Kbps greater throughput than without ARQ, but lead to the highest end-to-end delay for high bit error rate channels.

Based on the simulation results, we propose algorithms to maximize TCP/IP throughput and minimize end-to-end delay using the current bit error rate of the channel. We propose a metric, carrier-to-interference ratio (CIR) that is calculated from data retrieved from the broadband channel sounder. We propose algorithms using the carrier-to-interference ratio to control TCP/IP throughput and end-to-end delay.

The thesis also describes a monitor program to use in the broadband wireless system. The monitor program displays data collected from the broadband sounder and controls the settings for the data link layer protocol and broadband sounder while the network is in operation.
Master of Science

During the route discovery process, each node receiving the route request packet (RReq) will retransmit it exactly once. A distant neighbor may accidentally receive/loose the only RReq and use it to announce a new route, although that link is inferior/superior for route reply packets (RRep) or actual message routing. Overall, the constructed route may be far from the optimal. All existing route discovery schemes (including DSR/AODV) apply retransmission during route discovery exactly once (1R). Based on a realistic physical layer model, we propose two new route discovery schemes: n-retransmission (nR, retransmitting exactly n times) and n-retransmission c-reception (ncRR), retransmitting until we either reach a total of n own retransmissions or c copies from neighbors are heard. We compare our two new scheme with the traditional one, under otherwise identical conditions (same metric, same packet reception probability on each link) and the same choices about possibly retransmitting again upon discovering a better route (R+) or discarding it (R1), generating route reply packet for every received RRep (B*), or for first and better discovered routes only (B2), and retransmitting RRep exactly once (A1), up to a maximum of three times (A3), or optimally u times decided by link quality (Au). Experimental results show that the proposed ncRR scheme (for n=2 and c=3 or c=4) achieves the best tradeoff between quality of route, success rate and message overhead in the route discovery process, followed by the nR scheme, and both of them are superior to the existing traditional schemes.

When designing architectures and protocols for data traffic requiring real-time services, one of the major design goals is to guarantee that traffic deadlines can be met. However, many real-time applications also have additional requirements such as high throughput, high reliability, or energy efficiency. High-performance embedded systems communicating heterogeneous traffic with high bandwidth and strict timing requirements are in need of more efficient communication solutions, while wireless industrial applications, communicating control data, require support of reliability and guarantees of real-time predictability at the same time. To meet the requirements of high-performance embedded systems, this thesis work proposes two multi-wavelength high-speed passive optical networks. To enable reliable wireless industrial communications, a framework in­corporating carefully scheduled retransmissions is developed. All solutions are based on a single-hop star topology, predictable Medium Access Control algorithms and Earliest Deadline First scheduling, centrally controlled by a master node. Further, real-time schedulability analysis is used as admission control policy to provide delay guarantees for hard real-time traffic. For high-performance embedded systems an optical star network with an Arrayed Waveguide Grating placed in the centre is suggested. The design combines spatial wavelength re­use with fixed-tuned and tuneable transceivers in the end nodes, enabling simultaneous transmis­sion of both control and data traffic. This, in turn, permits efficient support of heterogeneous traf­fic with both hard and soft real-time constraints. By analyzing traffic dependencies in this mul­tichannel network, and adapting the real-time schedulability analysis to incorporate these traffic dependencies, a considerable increase of the possible guaranteed throughput for hard real-time traffic can be obtained. Most industrial applications require using existing standards such as IEEE 802.11 or IEEE 802.15.4 for interoperability and cost efficiency. However, these standards do not provide predict­able channel access, and thus real-time guarantees cannot be given. A framework is therefore de­veloped, combining transport layer retransmissions with real-time analysis admission control, which has been adapted to consider retransmissions. It can be placed on top of many underlying communication technologies, exemplified in our work by the two aforementioned wireless stan­dards. To enable a higher data rate than pure IEEE 802.15.4, but still maintaining its energy saving properties, two multichannel network architectures based on IEEE 802.15.4 and encompassing the framework are designed. The proposed architectures are evaluated in terms of reliability, utiliza­tion, delay, complexity, scalability and energy efficiency and it is concluded that performance is enhanced through redundancy in the time and frequency domains.

Cette thèse a pour but de modéliser les réseaux de capteurs sans fil à faible débit (WSN) basés sur la technique ultra bande étroite. Ce réseau a déjà été déployée par la société SIGFOX et a déjà démontré sa très grande efficacité pour les applications pour l’Internet des objets (IoTs) grâce à sa capacité de communication point à point efficace en terme de puissance consommée, et de sa connectivité de longue portée. Cette étude donne quelques aperçus sur le passage à l’échelle de la technique de l’UNB pour un réseau multipoint à point pour une liaison montante. L’accès au canal spécifique qui est basé sur l’accès multiple par répartition aléatoire de fréquence et de temps (R-FTDMA) est introduit et analysé. En outre, l’impact de l’interférence due à l’absence de stratégie d’ordonnancement à la couche MAC est étudié et modélisé. Notre modèle simplifié nous permet non seulement de décrire la puissance d’interférence agrégée, mais aussi d’évaluer les performances du système d’un tel réseau en matière de taux d’erreur et de probabilité de coupure. De même, la géométrie stochastique est utilisée pour modéliser la distribution spatiale des noeuds afin d’étendre le modèle simplifié dans le canal réaliste où les dégradations de canal sont prises en compte. De plus, le mécanisme de retransmission est considéré pour ce réseau. Cette étude permet de d’identifier le nombre optimal de retransmissions. Le réseau peut être configuré avec un paramètre global unique. Et enfin, cette thèse met en évidence le fait que le réseau de l’UNB Random-FTDMA est très pertinent dans un réseau réaliste, en particulier pour les applications à faible débit, car il allége le coût élevé du réseau, le coût de la synchronisation globale, mais sans perte de performance
This thesis aims at modeling the low-throughput wireless sensor networks (WSNs) based on ultra-narrow-band technology. Such wireless network is already been deployed by Sigfox company and has proved to be ultra-efficient for the Internet of things (IoTs) applications thanks to its ability of point-to-point communication in terms of power efficiency and long range connectivity. In particular, this thesis gives some insights on the scalability of UNB technology for a multi-point-to-point network in an uplink scenario. The multiple access schemes based on random time and frequency selection are introduced and analyzed. Furthermore, the interference impact due to the lack of scheduling strategy at the MAC layer is studied and modeled. Our simplified model using rectangular function allows us not only to describe the aggregate interference power but also evaluate the system performance of such network in terms of the bit-error-rate and outage probability. Besides, the geometry stochastic is used for spatial node distribution in order to extend the simplified model in the realistic channel communication where the channel impairments are taken into account. Besides, the retransmission mechanism is considered for such network. This study argues an optimal number of retransmission. The network can be configured with a unique global parameter. Last but not least, this thesis highlights the fact that the UNB network using Random-FTDMA schemes is very relevant in a realistic network, especially for low-throughput applications, because it bypasses the high network cost, the cost of global synchronization but without loss of performance

碩士
中原大學
電機工程研究所
98
Abstract Network coding is a technique which allows intermediate nodes to encode the receive messages before transmitting the information to other neighbors. Compared with traditional network transmission, it can improve the transmission throughput and reliability. Later T.Ho proposed Random Network coding and Sachin KattiKatabi proposed Opportunistic Network coding use different algorithms to achieve better performances. In 2009, Sameh Sorour and Shahrokh Valaee applied Network Coding on retransmission scheme, and proposed an adaptive scheme which combines Opportunistic Network Coding Retransmission Scheme (ONCR) and Random Network Coding Retransmission (RNCR) . The proposed can further improve the transmission throughput. We propose a simple ONCR algorithm to reduce the complexity and store the old received messages for current decoding to improve the system performances. The simulation shows the new method can achieve higher transmission throughput compared to the original one.

碩士
國立清華大學
資訊工程學系
90
The Medium Access Control (MAC) protocol of the IEEE 802.11 standard is based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). The basic retransmission mechanism, binary exponential backoff, may cause large packet delay and packet delay jitter that are not suitable for real-time traffic. In this thesis, we will first investigate some MAC enhancement mechanisms discussed in the IEEE 802.11 task group E, which was formed for enhancing the current 802.11 MAC protocol to support for applications with Quality of Service (QoS) requirements. Then, we will propose a jamming-based retransmission mechanism that is compatible with the 802.11 standard and could reduce the packet delay for real-time traffic. Besides, this mechanism performs stably when the traffic load is heavy. The optimal setting of our proposed mechanism is discussed analytically. We perform simulated experiments by comparing our proposed retransmission mechanism with the other two mechanisms discussed in the 802.11 task group E. We show that the jamming-based retransmission mechanism can reduce the packet delay and the packet dropping rate.

碩士
國立交通大學
網路工程研究所
103
With the popularity of smart phones, Long Term Evolution (LTE) has been developed. Since the downlink speed of LTE can be up to 100Mbps, increasing users download data by cell phones. Device-to-Device (D2D) communication is an important issue in LTE. The benefits of D2D communications are: User Equipments (UEs) can communicate directly, the system has a lower packet loss rate (PLR) and etc. We take advantage of D2D communications to do the retransmission, which is still a challenging topic. In this thesis, we develop a new D2D cooperative retransmission scheme to do the retransmission. We design an algorithm to find an optimal retransmission set which selects the ACKed UEs with a higher degree, lower repetition, higher remaining battery capacity as the retransmitters to retransmit the data to NACKed UEs, and the set of selected ACKed UEs is R, which can cover all NACKed UEs. The execution time of the algorithm is short and it can prolong the network lifetime. After data retransmission, eNB calculates the remaining battery capacity of the ACKed UEs, if their power level is lower than a predefined threshold (T), their retransmission power will be reduced to prolong the node lifetime. The simulation results show that our approach indeed has shorter execution time and a longer network lifetime.

In this paper, we propose an early retransmission scheme to improve TCP's performance in delivering time-sensitive media. Our extensive ns2 simulations show significant improvement. When integrated into a traditional TCP variant, namely TCP-SACK, the early retransmission scheme can substantially reduce the latency caused by retransmission timeout. As a result, it can help TCP-SACK achieve a considerably higher success rate in delivering real time media. Early Retransmission also enhances the performance of a delay-based TCP variant, namely PERT. Furthermore, we also explore the improvement brought by employing a fine-grained retransmission timer, and compare it with ER. We find out that ER outperforms the fine grained timer in a variety of conditions and the combination of the two can further improve performance.

碩士
國立中興大學
資訊科學與工程學系
103
In recent years, the middle-aged and the elderly with chronic diseases are increasing. Besides, the patient with chronic diseases does not cause health harm in a short period, and it does not need the long-term hospitalization. Thus, wireless body sensor network (WBAN) is the best scheme for daily care. According to the human physiological information, it not only gives the real-time notification to the user but also reduces the delay of a physician for detecting patients'' conditions. The physician early identifies the cause of disease to cure the disease. This thesis focuses on the retransmission problem for the shadowing sensors by the human body. The situation is caused from daily activities of a person with walk or run to shadow sensors. Therefore, in this thesis, I propose an efficient Cross-Layer Reliable Retransmission Scheme (CL-RRS) in IEEE 802.15.6. CL-RRS not only detects the information of the error frame to provide allocated resources, but it also predicts the actual period of shadowing sensors by the human body to reduce the number of the retransmission frame. Additionally, it increases the chance of successful transmission before the deadline of the frame to reduce power consumption.

碩士
國立中山大學
電機工程學系研究所
102
Multicast is an effective mechanism to save network bandwidth while transmitting real-time video streams in wireless networks. However, it lacks of a mechanism of error control. Packet errors happen easily because wireless channels are error-prone; this may bring a critical deterioration of the video quality. Besides, the end-to-end retransmission can not meet the strict delay constraint of a real-time video stream. In this thesis, we propose a multicast retransmission mechanism to improve the quality of real-time video streams over WiMAX network. In this mechanism, we design a MAC-layer ARQ scheme to retransmit the erroneous or lost ARQ blocks from BS, and consider three conditions, which are the bandwidth cost at retransmitting in multicast connection, the packet transmission delay and the acceptable delay constraint of MSs. We perform NS-3 simulation to demonstrate our proposed mechanism. The simulation results show that the mechanism can effectively reconstruct the quality of a real-time video stream at MSs. Furthermore, the cost of bandwidth using at retransmitting can be significantly reduced.

碩士
國立高雄第一科技大學
電腦與通訊工程所
96
With the evolution of mobile communication techniques, consumers are able to enjoy the convenience of transmitting multimedia data on mobile equipments. Recently, IEEE 802.16e system becomes one of very promising wireless broadband network systems. This system has wireless broadband, hi-capacity and long distance transmission merit. The multicast service is suggested in IEEE 802.16e standard. Multicast Service is the delivery of information to a group of destinations simultaneously using the most efficient strategy to deliver the data packets such as live MLB broadcast. Reliable multicast service supported by 802.16e is the one that multicast data packets must be transmitted to the multicast users without error. However, multicast data packets are often lost in wireless communications. Consequently, in reliable multicast services, retransmissions occur very frequently. To minimize the waste of radio resource, we propose two retransmission schemes, namely, Dedicated Retransmission with Selective Multicast Scheme (DR-SMS) and Dedicated Retransmission with Selective Multicast and Burst Hopping Scheme (DR-SMBHS), for reliable multicast services in IEEE 802.16e OFDMA systems. In comparison with existing Dedicated Retransmission Scheme (DRS), the DR-SMS and DR-SMBHS schemes can save downlink resources by 50% and 56%, respectively, and yield 11% and 19% more throughput gains than the DRS scheme, respectively.

碩士
國立交通大學
電信工程研究所
98
Due to the continuously increasing number of mobile multimedia uses, packet switch streaming would make much downlink resource be occupied. In order to make downlink resource be taken advantage more efficiently, multimedia broadcasting/multicasting service (MBMS) is proposed. In LTE, single frequency network can be further utilized to reinforce the coverage and the power of transmitting signal of MBMS. However, retransmission technique which is usually used to increase data robustness is hard to realize in broadcasting/multicasting. If unicast retransmission technique works in broadcasting/multicasting, it would result in the waste of downlink resource. In this thesis, we propose the retransmission scheme which takes advantage of feedback channel and grouping of mobile users to strike a balance between data block error rate and retransmission rate. Additionally, we propose two kinds of feedback channel assignment to pursue more flexible assignment. We have two ways to let base station judge whether the retransmission will be performed or not. First one is based on threshold, and the second one is based on probability. In simulation, the proposed scheme indeed decreases retransmission rate with acceptable data block error rate. Besides, goodput of proposed is larger than the compared schemes.