Performance Evaluation of Wireless Medium Access Control Protocols for Internet of Things

The Internet of Things makes the residents in Smart Cities enjoy a more efficient and high-quality lifestyle by wirelessly interconnecting the physical and visual world. However, the performance of wireless networks is challenged by the ever-growing wireless traffic data, the complexity of the network structures, and various requirements of Quality of Service (QoS), especially on the Internet of Vehicle and wireless sensor networks. Consequently, the IEEE 802.11p and 802.11ah standards were designed to support effective inter-vehicle communications and large-scale sensor networks, respectively. Although their Medium Access Control protocols have attracted much research interest, they have yet to fully consider the influences of channel errors and buffer sizes on the performance evaluation of these Medium Access Control (MAC) protocols. Therefore, this thesis first proposed a new analytical model based on a Markov chain and Queuing analysis to evaluate the performance of IEEE 802.11p under imperfect channels with both saturated and unsaturated traffic. All influential factors of the Enhanced Distributed Channel Access (EDCA) mechanism in IEEE 802.11p are considered, including the backoff counter freezing, Arbitration Inter-Frame Spacing (AIFS) defers, the internal collision, and finite MAC buffer sizes. Furthermore, this proposed model considers more common and actual conditions with the influence of channel errors and finite MAC buffer sizes. The effectiveness and accuracy of the developed model have been validated through extensive ns-3 simulation experiments. Second, this thesis proposes a developed analytical model based on Advanced Queuing Analysis and the Gilbert-Elliot model to analyse the performance of IEEE 802.11p with burst error transmissions. This proposed analytical model simultaneously describes transmission queues for all four Access Categories (AC) queues with the influence of burst errors. Similarly, this presented model can analyse QoS performance, including throughputs and end-to-end delays with the unsaturated or saturated load traffics. Furthermore, this model operates under more actual bursty error channels in vehicular environments. In addition, a series of simulation experiments with a natural urban environment is designed to validate the efficiency and accuracy of the presented model. The simulation results reflect the reliability and effectiveness of the presented model in terms of throughput and end-to-end delays under various channel conditions. Third, this thesis designed and implemented a simulation experiment to analyse the performance of IEEE 802.11ah. These simulation experiments are based on ns-3 and an extension. These simulation experiments' results indicate the Restricted Access Window (RAW) mechanism's influence on the throughputs, end-to-end delays, and packet loss rates. Furthermore, the influences of channel errors and bursty errors are considered in the simulations. The results also show the strong impact of channel errors on the performance of IEEE 802.11ah due to urban environments. Finally, the potential future work based on the proposed models and simulations is analysed in this thesis. The proposed models of IEEE 802.11p can be an excellent fundamental to optimise the QoS due to the precise evaluation of the influence of factors on the performance of IEEE 802.11p. Moreover, it is possible to migrate the analytical models of IEEE 802.11p to evaluate the performance of IEEE 802.11ah

A Fully-Integrated Reconfigurable Dual-Band Transceiver for Short Range Wireless Communications in 180 nm CMOS

© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.A fully-integrated reconfigurable dual-band (760-960 MHz and 2.4-2.5 GHz) transceiver (TRX) for short range wireless communications is presented. The TRX consists of two individually-optimized RF front-ends for each band and one shared power-scalable analog baseband. The sub-GHz receiver has achieved the maximum 75 dBc 3rd-order harmonic rejection ratio (HRR3) by inserting a Q-enhanced notch filtering RF amplifier (RFA). In 2.4 GHz band, a single-ended-to-differential RFA with gain/phase imbalance compensation is proposed in the receiver. A ΣΔ fractional-N PLL frequency synthesizer with two switchable Class-C VCOs is employed to provide the LOs. Moreover, the integrated multi-mode PAs achieve the output P1dB (OP1dB) of 16.3 dBm and 14.1 dBm with both 25% PAE for sub-GHz and 2.4 GHz bands, respectively. A power-control loop is proposed to detect the input signal PAPR in real-time and flexibly reconfigure the PA's operation modes to enhance the back-off efficiency. With this proposed technique, the PAE of the sub-GHz PA is improved by x3.24 and x1.41 at 9 dB and 3 dB back-off powers, respectively, and the PAE of the 2.4 GHz PA is improved by x2.17 at 6 dB back-off power. The presented transceiver has achieved comparable or even better performance in terms of noise figure, HRR, OP1dB and power efficiency compared with the state-of-the-art.Peer reviewe

Nonlinear impairments and mitigation technologies for the next generation fiber-wireless mobile fronthaul networks

The proliferation of Internet-connected mobile devices and video-intensive services are driving the growth of mobile data traffic in an explosive way. The last mile of access networks, mobile fronthaul (MFH) networks, have become the data rate bottleneck of user experience. The objective of this research are two-fold. For analog MFH, nonlinear interferences among multiple bands of mobile signals in a multi-RAT multi-service radio-over-fiber (RoF)-based MFH system are investigated for the first time. The nonlinear impairments of both single-carrier and multi-carrier signals are investigated, and it is experimentally demonstrated that inter-channel interferences play a more important role in the performance degradation of analog MFH than the nonlinear distortions of each individual signal. A digital predistortion technique was also presented to linearize the analog MFH links. On the other hand, for digital MFH, we experimentally demonstrate a novel digitization interface based on delta-sigma modulation to replace the state-of-the-art common public radio interface (CPRI). Compared with CPRI, it provides improved spectral efficiency and enhanced fronthaul capacity, and can accommodate both 4G-LTE and 5G mobile services.Ph.D

Implementação do protocolo IEEE 802.11ah através de rádio definido por software

O crescente uso de redes conhecidas como Internet das Coisas (IoT) constitui oportunidade para um vasto campo de pesquisa e desenvolvimento, onde diversos protocolos oferecem soluções práticas distintas. Entre estes, o protocolo IEEE 802.11ah é uma alternativa de livre implementação que utiliza uma faixa de espectro não licenciada abaixo de 1 GHz. Este trabalho oferece contribuições para a implementação de técnicas de comunicação adequadas a redes de sensores sem fio (WSN) baseadas no padrão IEEE 802.11ah (Wi-Fi HaLow). De forma a facilitar trabalhos futuros de pesquisa e devido a baixa disponibilidade de dispositivos comerciais, uma plataforma de rádio definido por software foi utilizada para realizar a implementação de um enlace em camada física a partir da especificação do protocolo e de uma implementação pré-existente que comtempla as características de modulação fundamentais do protocolo. Foram conduzidos testes e experimentos de bancada para avaliar o desempenho dos dispositivos, em situações de interferência e ruído. As condições de interferência foram um sinal senoidal, um sinal LoRa e um sinal O-QPSK derivado do protocolo IEEE 802.15.4, uma vez que ocupam a mesma banda de frequências do protocolo avaliado. Também foi avaliada a rejeição a sinais interferente IEEE 802.11ah sobrepostos no mesmo canal, em canal adjacente e em canal não adjacente. As simulações e experimentos geraram um conjunto de dados que foram analisados conforme os requisitos da especificação e da literatura, atendendo o desempenho especificado. Os valores limites para estas interferências são demonstrados em termos de diferenças de potências. O código-fonte será disponibilizado publicamente, para servir de base a trabalhos futuros que tenham por objetivo avaliar o desempenho do protocolo IEEE 802.11ah sob outros aspectos ou provar ideias teóricas inovadoras que, embora propostas e demonstradas de forma simulada, por vezes não encontram comprovação em hardware.The Internet of Things (IoT) environment is an expanding field with many competing standards solving various communication challenges. However, interesting theoretical propositions, demonstrated in simulations during research, end up not getting a quick implementation in hardware. This work provides contributions towards an implementation of the IEEE 802.11ah (Wi-Fi HaLow) standard, an extension of the Wi-Fi protocol focused on providing IoT-like connectivity on midrange sites (up to 1 km). A softwaredefined radio plataform, programmed with open-source software, is used to provide an extensible code base, derived from existing works. Simulation and experimental measurements were conducted towards evaluating the performance and limitations in interference and noise environments. As interference, sinusoidal, LoRa and IEEE 802.15.4 O-QPSK derived signals were used as to evaluate the minimum difference of powers necessary to garantee the IEEE 802.11ah signal is received and correctly decoded with 90 % packet delivery rate. Adjacent, non adjacent and same channel rejection were also evaluated. All results agree with the requirements presented in the standard. We make the source code freely available in the Internet as to enable future modifications and derived works