IEEE 802.16e 에서 멀티캐스트 MAP 의 효율적 전송 기법

The IEEE 802.16e suggests the use of multicast sub-MAPs whose messages are differently encoded according to the operating condition. In this case, it is desired for the base station to properly choose a modulation and coding set (MCS) associated with operating condition. In this paper, we consider the use of an adaptive modulation coding (AMC) scheme for the multicast sub-MAP that achieves the same MAP coverage as the broadcast MAP while minimizing the signaling overhead. We consider the adjustment of the threshold for the AMC according to the channel condition without explicit information on the channel condition, significantly reducing the amount of the signaling overhead. Simulation results show that when it is applied to voice-over-IP (VoIP) services, the proposed scheme can enhance the VoIP capacity

Physical and MAC Layer Design for Active Signaling Schemes in Vehicular Networks

International audienceNowadays, many telecommunication systems (wifi, cable systems and 4G, 5G cellular networks) use Orthogonal Frequency Division Multiplexing (OFDM) as the physical layer standard. The design of efficient OFDM signal detection algorithms is very important to provide reliable systems, and this is particularly true for Vehicular Adhoc Networks (VANETs) involving autonomous vehicles, where missing a signal or detecting a fake one may cause a dangerous situation. The performance of these algorithms is generally evaluated in terms of their robustness against noise. In this paper, we evaluate the probability of error in signal detection in order to establish the minimum length of preamble needed for the active signaling process. This mechanism is used in AS-DTMAC (active signaling fully distributed TDMA-based MAC protocol) to reduce access collisions. Thus, by reducing the length of the preamble, greater time is given for the payload part of the packet, resulting in increased throughput

Implementing WiFi ax in SDR

Both Carrier Sensing Multiple Access (CSMA) and Orthogonal Frequency Division Multiple Access (OFDMA) are vital techniques for WiFi radio operations. CSMA deals with decentralized sharing of the medium, and OFDMA deals with dividing up the channel into multiple smaller allocations of the channel to transmit data from multiple users simultaneously. OFDMA is a new multiple access scheme introduced in the upcoming IEEE 802.11ax standard. This paper details research with Dr. Bae in implementing portions of the upcoming 802.11ax standard using software defined radio. First, this paper provides in-depth setup information for the Wime Project and explains the Wime Project implementation in great detail. Second, this paper provides pseudo code for how to implement CSMA and an attempt at implementing OFDMA

Reliable Packet Detection for Random Access Networks: Analysis, Benchmark, and Optimization

This paper reexamines and fundamentally improves the Schmidl-and-Cox (S&C) algorithm, which is extensively used for packet detection in wireless networks, and enhances its adaptability for multi-antenna receivers. First, we introduce a new "compensated autocorrelation" metric, providing a more analytically tractable solution with precise expressions for false-alarm and missed-detection probabilities. Second, this paper proposes the Pareto comparison principle for fair benchmarking packet-detection algorithms, considering both false alarms and missed detections simultaneously. Third, with the Pareto benchmarking scheme, we experimentally confirm that the performance of S&C can be greatly improved by taking only the real part and discarding the imaginary part of the autocorrelation, leading to the novel real-part S&C (RP-S&C) scheme. Fourth, and perhaps most importantly, we utilize the compensated autocorrelation metric we newly put forth to extend the single-antenna algorithm to multi-antenna scenarios through a weighted-sum approach. Two optimization problems, minimizing false-alarm and missed-detection probabilities respectively, are formulated and solutions are provided. Our experimental results reveal that the optimal weights for false alarms (WFA) scheme is more desirable than the optimal weights for missed detections (WMD) due to its simplicity, reliability, and superior performance. This study holds considerable implications for the design and deployment of packet-detection schemes in random-access networks

The manipulation of RF-DNA fingerprints through the use of a phase-modulated clock in IEEE802.11a Wi-Fi signals

The ubiquity of IoT devices has created an urgent need to augment existing network security mechanisms by leveraging discriminating, waveform characteristics to facilitate the detection of unauthorized devices. RF-DNA fingerprints are a waveform-based approach capable of distinguishing one device from others of the same manufacturer and model. This work investigates the extent to which the intentionally inserted changes can alter the RF-DNA fingerprints of the transmitted signal without negatively impacting the receiver’s ability to demodulate the received signal. The experiments presented herein investigate intentional changes caused by the external clock to the preamble of the 802.11a Wi-Fi waveform from which RF-DNA fingerprints are extracted. Analysis is conducted using the Gabor Transform. The results show the structure of the preamble remains intact when the clock signal is phase-modulated using sine waves oscillating frequencies up to 10 kHz with deviation of 1.5 degrees, or 2.5 kHz with deviation of 90 degrees

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

Secure short-range communications

Analysts predict billions of everyday objects will soon become ``smart’\u27 after designers add wireless communication capabilities. Collectively known as the Internet of Things (IoT), these newly communication-enabled devices are envisioned to collect and share data among themselves, with new devices entering and exiting a particular environment frequently. People and the devices they wear or carry may soon encounter dozens, possibly hundreds, of devices each day. Many of these devices will be encountered for the first time. Additionally, some of the information the devices share may have privacy or security implications. Furthermore, many of these devices will have limited or non-existent user interfaces, making manual configuration cumbersome. This situation suggests that devices that have never met, nor shared a secret, but that are in the same physical area, must have a way to securely communicate that requires minimal manual intervention. In this dissertation we present novel approaches to solve these short-range communication issues. Our techniques are simple to use, secure, and consistent with user intent. We first present a technique called Wanda that uses radio strength as a communication channel to securely impart information onto nearby devices. We focus on using Wanda to introduce new devices into an environment, but Wanda could be used to impart any type of information onto wireless devices, regardless of device type or manufacturer. Next we describe SNAP, a method for a single-antenna wireless device to determine when it is in close physical proximity to another wireless device. Because radio waves are invisible, a user may believe transmissions are coming from a nearby device when in fact the transmissions are coming from a distant adversary attempting to trick the user into accepting a malicious payload. Our approach significantly raises the bar for an adversary attempting such a trick. Finally, we present a solution called JamFi that exploits MIMO antennas and the Inverse-Square Law to securely transfer data between nearby devices while denying more distant adversaries the ability to recover the data. We find JamFi is able to facilitate reliable and secure communication between two devices in close physical proximity, even though they have never met nor shared a key