Interference management using one bit feedback

This paper studies the performance of quasi-static spectrum sharing networks utilizing one bit interference indicator feedback. Assuming no channel state information at the transmitters, the channel average rate is obtained under different power allocation strategies. Simulation results show that interference indicator feedback leads to considerable rate increment even with no transmitter channel state information

On the Average Rate of HARQ-Based Quasi-Static Spectrum Sharing Networks

Spectrum sharing networks are communication setups in which unlicensed secondary users are permitted to work within the spectrum resources of primary licensees. Considering quasi-static fading environments, this paper studies the effect of hybrid automatic repeat request (HARQ) feedback on the average rate of unlicensed spectrum sharing channels. The results are obtained for different scenarios; Under both peak and average secondary user transmission power constraints, the channel average rate is determined under primary user limited received interference power conditions when there is perfect information about the interference available at the secondary user transmitter. An approximate solution for power allocation between incremental redundancy (INR) HARQ-based data retransmissions is proposed which can be applied in single-user networks as well. Then, we investigate the effect of imperfect secondary-primary channel state information on the interference-limited average rate of the secondary channel. Finally, we restudy all mentioned scenarios in the case where the data transmission is constrained to have limited outage probability. Substantial performance improvement is observed with even a single HARQ-based retransmission in all simulations

Valutazione di schemi di trasmissione basati su SR-ARQ

Questa tesi propone uno studio di alcune tecniche di correzione degli errori, basate sul meccanismo Selective Repeat – Automatic Repeat reQuest (SR-ARQ), per analizzare le prestazioni degli schemi, con particolare riferimento al caso di lunghi tempi di propagazione. Mettiamo a confronto l’SR-ARQ con 2 varianti dello stesso, Double Selective Repeat (2SR-ARQ) e Second Replica Selective Repeat (SR2-ARQ). Facciamo così uno studio approssimato sul ritardo medio di consegna (delivery delay, mdelay) di un pacchetto in particolare, quello centrale rispetto a una finestra di larghezza m slots (spazi). La valutazione si basa su uno studio analitico originale, nel quale vengono ricavati risultati numerici che vengono discussi e illustrat

SR ARQ packet delay statistics on Markov channels in the presence of variable arrival rate

In this letter we investigate the packet delay statistics of a fully reliable Selective Repeat ARQ scheme by considering a Discrete Time Markov Channel with non-instantaneous feedback and assigned round-trip delay m. Our focus is on studying the impact of the arrival process on the delay experienced by a packet. An exact model is introduced to represent the system constituted by the transmitter buffer, the m round-trip slots, and the channel state. By means of this model, we evaluate and discuss the delay statistics and we analyze the impact of the system parameters, in particular the packet arrival rate, on the delay statistics

Cross-layer per-flow QoE evaluation for VoIP in wireless system

The Internet as the biggest worldwide network provides a huge range of facilities and conveniences. Different types of communication applications are one of the most manifest conveniences provided up to date. Among others wireless VoIP as one of the most adhered applications which compliances anywhere/anytime communication capability is of special interest and attention. Performance optimization in the context of real-time applications such as VoIP is one of the most principal and yet challenging issues. Wireless environments aggravate conditions and tensity of issues due to inherent uncertainties, vulnerabilities and time-varying characteristics. The layered structure of the communication protocol stack is not well-suited for wireless environments by setting isolated layers and encumbering limitations. Whereas, if different layers of the protocol stack not only neighbouring ones can communicate and exchange information and make appropriate functionality decisions based on obtained information may be it becomes more straightforward to achieve optimized performance at any given instant of time. This is the basis for cross-layer design. In this thesis work we proposed a cross-layer performance evaluation frame work for a wireless VoIP flow of interest from the end-user perspective. As, quality perception is the most momentous aspect of it. In this frame work we used the E-model for formulating and measurement of perceived speech quality. In our work we considered the effect of underlying layers parameters and processes contributing in performance evaluation on the performance provided to the IP layer. As, performance evaluation is carried out at the IP layer. IP packet loss probability and transmission delay as the effects of the wireless channel, FEC and ARQ error concealment mechanisms at the data-link layer, queuing process at the IP layer, losses due to buffer overflow and at the end perceived quality evaluation through simple packet loss rate model and the integrated loss metric model (Clark s model) were considered through extensive simulations. We realized that the Clark s model which takes into account the effect of loss correlation provides more accurate performance estimates. As a general and important result we concluded that by designing and developing dynamic performance control systems such as rate control or resource allocation which dynamically adapt to time-varying real-time traffic and wireless channel conditions we can achieve better performance at any given instant of time. This can be considered as further studies and as an extension of this thesis work. /Kir1

Towards reliable communication in LTE-A connected heterogeneous machine to machine network

Machine to machine (M2M) communication is an emerging technology that enables heterogeneous devices to communicate with each other without human intervention and thus forming so-called Internet of Things (IoTs). Wireless cellular networks (WCNs) play a significant role in the successful deployment of M2M communication. Specially the ongoing massive deployment of long term evolution advanced (LTE-A) makes it possible to establish machine type communication (MTC) in most urban and remote areas, and by using LTE-A backhaul network, a seamless network communication is being established between MTC-devices and-applications. However, the extensive network coverage does not ensure a successful implementation of M2M communication in the LTE-A, and therefore there are still some challenges. Energy efficient reliable transmission is perhaps the most compelling demand for various M2M applications. Among the factors affecting reliability of M2M communication are the high endto-end delay and high bit error rate. The objective of the thesis is to provide reliable M2M communication in LTE-A network. In this aim, to alleviate the signalling congestion on air interface and efficient data aggregation we consider a cluster based architecture where the MTC devices are grouped into number of clusters and traffics are forwarded through some special nodes called cluster heads (CHs) to the base station (BS) using single or multi-hop transmissions. In many deployment scenarios, some machines are allowed to move and change their location in the deployment area with very low mobility. In practice, the performance of data transmission often degrades with the increase of distance between neighboring CHs. CH needs to be reselected in such cases. However, frequent re-selection of CHs results in counter effect on routing and reconfiguration of resource allocation associated with CH-dependent protocols. In addition, the link quality between a CH-CH and CH-BS are very often affected by various dynamic environmental factors such as heat and humidity, obstacles and RF interferences. Since CH aggregates the traffic from all cluster members, failure of the CH means that the full cluster will fail. Many solutions have been proposed to combat with error prone wireless channel such as automatic repeat request (ARQ) and multipath routing. Though the above mentioned techniques improve the communication reliability but intervene the communication efficiency. In the former scheme, the transmitter retransmits the whole packet even though the part of the packet has been received correctly and in the later one, the receiver may receive the same information from multiple paths; thus both techniques are bandwidth and energy inefficient. In addition, with retransmission, overall end to end delay may exceed the maximum allowable delay budget. Based on the aforementioned observations, we identify CH-to-CH channel is one of the bottlenecks to provide reliable communication in cluster based multihop M2M network and present a full solution to support fountain coded cooperative communications. Our solution covers many aspects from relay selection to cooperative formation to meet the user’s QoS requirements. In the first part of the thesis, we first design a rateless-coded-incremental-relay selection (RCIRS) algorithm based on greedy techniques to guarantee the required data rate with a minimum cost. After that, we develop fountain coded cooperative communication protocols to facilitate the data transmission between two neighbor CHs. In the second part, we propose joint network and fountain coding schemes for reliable communication. Through coupling channel coding and network coding simultaneously in the physical layer, joint network and fountain coding schemes efficiently exploit the redundancy of both codes and effectively combat the detrimental effect of fading conditions in wireless channels. In the proposed scheme, after correctly decoding the information from different sources, a relay node applies network and fountain coding on the received signals and then transmits to the destination in a single transmission. Therefore, the proposed schemes exploit the diversity and coding gain to improve the system performance. In the third part, we focus on the reliable uplink transmission between CHs and BS where CHs transmit to BS directly or with the help of the LTE-A relay nodes (RN). We investigate both type-I and type-II enhanced LTE-A networks and propose a set of joint network and fountain coding schemes to enhance the link robustness. Finally, the proposed solutions are evaluated through extensive numerical simulations and the numerical results are presented to provide a comparison with the related works found in the literature