Optimum Design of Spectral Efficient Green Wireless Communications

This dissertation focuses on the optimum design of spectral efficient green wireless communications. Energy efficiency (EE), which is defined as the inverse of average energy required to successfully deliver one information bit from a source to its destination, and spectral efficiency (SE), which is defined as the average data rate per unit bandwidth, are two fundamental performance metrics of wireless communication systems. We study the optimum designs of a wide range of practical wireless communication systems that can either maximize EE, or SE, or achieve a balanced tradeoff between the two metrics. There are three objectives in this dissertation. First, an accurate frame error rate (FER) expression is developed for practical coded wireless communication systems operating in quasi-static Rayleigh fading channels. The new FER expression enables the accurate modeling of EE and SE for various wireless communication systems. Second, the optimum designs of automatic repeat request (ARQ) and hybrid ARQ (HARQ) systems are performed to by using the EE and SE as design metrics. Specifically, a new metric of normalized EE, which is defined as the EE normalized by the SE, is proposed to achieve a balanced tradeoff between the EE and SE. Third, a robust frequency-domain on-off accumulative transmission (OOAT) scheme has been developed to achieve collision-tolerant media access control (CT-MAC) in a wireless network. The proposed frequency domain OOAT scheme can improve the SE and EE by allowing multiple users to transmit simultaneously over the same frequency bands, and the signal collisions at the receiver can be resolved by using signal processing techniques in the physical layer

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

Mecanismos de HARQ usando códigos LDPC com retransmissão parcial e combinação por diversidade

Modern standards of communication systems are including in their standards retransmission mechanisms. This work presents mechanisms for retransmission of packets by simpler and more efficient than the classical mechanisms of packet retransmissions. The proposed schemes are presented that use packet retransmission with partial retransmission and diversity combining. In addition, theoretical analysis will be presented to validate the results of the simulations. These theoretical analysis are obtained through the analysis EXIT charts and mutual information. The results and analysis were performed on channels such as AWGN and Block-Fading. The computational complexity, ease implementation and low average energy consumption for transmission of the proposed methods are some of the reasons they become interesting both for academia and for industry.Os recentes padrões de sistemas de comunicação estão incluindo em suas normas mecanismos de retransmissão de pacotes. Este trabalho apresenta mecanismos de retransmissão de pacotes de formas simples e mais eficientes do que os mecanismos clássicos de retransmissão de pacotes. São apresentados esquemas de retransmissão de pacotes que utilizam retransmissões parciais e combinação por diversidade. Além disso, serão apresentadas análises teóricas para validar os resultados obtidos das simulações. Estas análises teóricas são obtidas através das análises de EXIT charts e da informação mútua. Os resultados e análises foram realizados em canais do tipo AWGN e com desvanecimento por blocos (Block-Fading). A complexidade computacional, facilidade de implementação e baixo consumo médio de energia por transmissão dos métodos propostos são alguns dos motivos pelos quais, tornam-se interessantes tanto para a área acadêmica quanto para a indústria

Link Adaptation Criteria for Multicarrier Signaling on Doubly-selective Wireless Channels

In this thesis we investigate some link adaptation criteria basically in terms of word error rate estimate. Our goal is to obtain a classification of the existent effective SNR mapping (ESM) methods and to further propose some possible new alternatives, taking into account their impact on the final link adaptation performances. HARQ technique has been finally applied to guarantee the desired quality of service

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

Cooperative retransmission protocols in fading channels : issues, solutions and applications

Future wireless systems are expected to extensively rely on cooperation between terminals, mimicking MIMO scenarios when terminal dimensions limit implementation of multiple antenna technology. On this line, cooperative retransmission protocols are considered as particularly promising technology due to their opportunistic and flexible exploitation of both spatial and time diversity. In this dissertation, some of the major issues that hinder the practical implementation of this technology are identified and pertaining solutions are proposed and analyzed. Potentials of cooperative and cooperative retransmission protocols for a practical implementation of dynamic spectrum access paradigm are also recognized and investigated. Detailed contributions follow. While conventionally regarded as energy efficient communications paradigms, both cooperative and retransmission concepts increase circuitry energy and may lead to energy overconsumption as in, e.g., sensor networks. In this context, advantages of cooperative retransmission protocols are reexamined in this dissertation and their limitation for short transmission ranges observed. An optimization effort is provided for extending an energy- efficient applicability of these protocols. Underlying assumption of altruistic relaying has always been a major stumbling block for implementation of cooperative technologies. In this dissertation, provision is made to alleviate this assumption and opportunistic mechanisms are designed that incentivize relaying via a spectrum leasing approach. Mechanisms are provided for both cooperative and cooperative retransmission protocols, obtaining a meaningful upsurge of spectral efficiency for all involved nodes (source-destination link and the relays). It is further recognized in this dissertation that the proposed relaying-incentivizing schemes have an additional and certainly not less important application, that is in dynamic spectrum access for property-rights cognitive-radio implementation. Provided solutions avoid commons-model cognitive-radio strict sensing requirements and regulatory and taxonomy issues of a property-rights model