Analysis of asymmetry of traffic in full-duplex wireless local area network

Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do ParanáThe standard commodity wireless hardware is half-duplex because there are challenges in full-duplex wireless that need attention and improvement. The self-interference in radios is one of the big challenges, but, even though there is no standard yet, there are several proposals that cancel enough self-interference that it is possible for communication to be successfully made. The standard half-duplex rules of the media access control (MAC) protocol contained on wireless cards do not accept simultaneous transmissions, because simultaneous transmissions are likely to collide with each other. Therefore, full-duplex wireless networks need a new MAC protocol to be able to handle the different full-duplex transmissions, namely, symmetric and asymmetric. Symmetric full-duplex transmissions ocurr between just two stations, which can be managed trivially by a suitable MAC protocol. On the other hand, asymmetric transmissions occur in communications involving three stations, and those transmissions are likely to produce collisions if one station receives simultaneously signals from the two others. From the different difficulties of each transmission type, emerges the doubt about how many opportunities are there for a full-duplex wireless network to make each type of transmission. With the focus on this question, this research proposes a method to collect traffic data from a real half-duplex wireless local area network (WLAN) to measure the amount of full-duplex symmetric and asymmetric transmission opportunities. The proposed method relies on: the brcmfmac driver, to collect the traffic data in kernel space; the Ftrace tracing utility framework, to send the data from kernel to user space; a Raspberry Pi 3 B+, in which is installed the modified driver and tracing utility; and an estimate of the travel time of frames between the kernel and firmware. The results of this research include a method to collect traffic data with the goal of measuring the amount of full-duplex transmissions opportunities and their types in a real half-duplex WLAN. It is also presented the analysis of a small amount of data collected during four days as an example of the proposed method, which shows that 4.096% of the frames presented the proper conditions to symmetric transmissions, while only 0.025% in the case of asymmetric transmissions.Os dispositivos sem fio padrão são half-duplex, pois o full-duplex sem fio apresenta desafios que precisam receber atenção e melhorias. A auto-interferência presente é um dos desafios, mas, ainda que não haja padrão, existem algumas propostas que cancelam a auto-interferência a ponto de comunicações serem realizadas com sucesso. As regras padrão do protocolo de controle de acesso ao meio (MAC) half-duplex contido nas placas sem fio não permitem transmissões simultâneas, já que são propensas a causar colisões. Portanto, redes full-duplex sem fio precisam de um novo protocolo MAC para que os diferentes tipos de transmissão full-duplex (simétrico e assimétrico) sejam utilizados. As transmissões simétricas ocorrem em comunicações entre apenas duas estações, o que pode ser gerido de forma trivial por um protocolo MAC apropriado. Por outro lado, as transmissões assimétricas envolvem comunicações entre três estações, e estas transmissões são propensas a gerar colisões no caso de uma das estações receber sinal das outras duas, simultaneamente. Devido às diferentes dificuldades de cada tipo de transmissão, surge a dúvida sobre quantas oportunidades existem para comunicação full-duplex de cada tipo de transmissão. Com foco nessa questão, esta pesquisa propõe um método para coleta de dados de tráfego de uma rede de área local sem fio (WLAN) half-duplex com o objetivo de calcular a quantidade de oportunidades de transmissões full-duplex simétricas e assimétricas. O método proposto conta com: o driver brcmfmac, para coleta de dados de tráfego em ambiente de kernel; o Ftrace, ferramenta utilitária de rastreamento, usado para enviar os dados do kernel para o ambiente do usuário; um Raspberry Pi 3 B+, no qual é instalado o driver modificado e o utilitário de rastreamento; e, um cálculo para estimar o tempo de viagem de pacotes entre o kernel e o firmware. Os resultados desta pesquisa incluem um método de coleta de dados de tráfego com o objetivo de quantificar as oportunidades de transmissões full-duplex e seus tipos em uma WLAN real. Também é apresentado uma coleta feita por quatro dias como um exemplo do mesmo. A análise mostra que 4.096% dos pacotes apresentam condições adequadas para transmissões simétricas, e apenas 0.025% para transmissões assimétricas

Beam-Space MIMO Radar for Joint Communication and Sensing with OTFS Modulation

Motivated by automotive applications, we consider joint radar sensing and data communication for a system operating at millimeter wave (mmWave) frequency bands, where a Base Station (BS) is equipped with a co-located radar receiver and sends data using the Orthogonal Time Frequency Space (OTFS) modulation format. We consider two distinct modes of operation. In Discovery mode, a single common data stream is broadcast over a wide angular sector. The radar receiver must detect the presence of not yet acquired targets and perform coarse estimation of their parameters (angle of arrival, range, and velocity). In Tracking mode, the BS transmits multiple individual data streams to already acquired users via beamforming, while the radar receiver performs accurate estimation of the aforementioned parameters. Due to hardware complexity and power consumption constraints, we consider a hybrid digital-analog architecture where the number of RF chains and A/D converters is significantly smaller than the number of antenna array elements. In this case, a direct application of the conventional MIMO radar approach is not possible. Consequently, we advocate a beam-space approach where the vector observation at the radar receiver is obtained through a RF-domain beamforming matrix operating the dimensionality reduction from antennas to RF chains. Under this setup, we propose a likelihood function-based scheme to perform joint target detection and parameter estimation in Discovery, and high-resolution parameter estimation in Tracking mode, respectively. Our numerical results demonstrate that the proposed approach is able to reliably detect multiple targets while closely approaching the Cramer-Rao Lower Bound (CRLB) of the corresponding parameter estimation problem.Comment: 33 Page