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Communications Society The Long Island Chapter of the Communications Society (COM-19) serves LI technical professionals and businesses in the communications industry by providing lectures and seminars on various communications topics, including smart-antenna technology, position location, data communications, mobile communications, and homeland-security applications. Please contact us if you have any suggestions. For
upcoming Communications Society lectures, please visit the calendar page. |
Organizations > CEWIT > LI Wireless Historical Society Publications > CED Reference Tutorials |
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Past Lectures |
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The theory and practice of advanced modem technology suitable for high data rate wireless communication is discussed. Topics covered include antennas, field propagation, networking management and security. A focus is provided on satellite communication networks which are now an indispensable part of most major telecommunication systems. Satellites offer a number of features not readily available through other means, such as access to remote communities. The Organization of Standards establishes and regulates international standards ensuring worldwide compatibility.
Phase noise is a critical parameter in modern digital communications system designs. As modulation techniques became more complex to maximize the utilization of the available bandwidth, phase noise became an important limiting factor in the performance of a communication link. Inherent in all active functions, but usually critical in oscillators, phase noise like normalized thermal noise is an interference signal that cannot be eliminated or improved and continues to degrade a signal as it moves through the communications link. Because phase noise is greatest close to the carrier, unlike thermal noise, it cannot be filtered to improve the system performance. Part 1 of this lecture series focuses on the basic concepts necessary to understand phase noise, the relationship between thermal noise and phase noise, the concept of oscillator stability and how it relates to phase noise, the origin of phase noise in oscillators, and the spectral characteristics of phase noise.
This lecture focuses on the equipment specifications and how they affect the communications channel. The lecture starts off with explaining what constitutes an ideal signal transmission channel, the requirements of non-interference, digital symbol recovery, and digital bit recovery. The signal interference problem is defined in the frequency domain, digital symbol recovery is defined in terms of Error Vector Measurements (EVM), and the digital bit recovery problem is analyzed in the time domain using the concept of "Eye Diagrams". The non-ideal signal channel characteristics are related to system specification and examples are given relating systems specifications to Bit Error Rates (BER). These techniques are applicable to all advanced communication systems, applicable to terrestrial and satellite communications, as well as wired and Fiber Optic communication systems.
This lecture focuses on the modulation techniques used in Satellite Communications. Starting with the fundamentals of analog modulation originally used, the lecture then goes into digital modulation techniques currently employed and more advanced digital modulation constellations in the planning stage. Discussed are the digital constellations, quantizing considerations, constant amplitude techniques, quadrature amplitude modulation techniques, bandwidth considerations, implementation topologies, design tradeoffs, and other related considerations. The same techniques are used in other advanced communication systems and are therefore applicable to terrestrial as well as satellite communications.
With the advent of WiFi devices using MIMO (Multiple Input Multiple Output) technologies, there is considerable interest in understanding how this technology works and its future evolution. A very promising variation is "virtual MIMO" or cooperative communications, which promises MIMO-like performance from small single antenna wireless devices (MIMO typically requires larger devices that can accommodate multiple antennas). There is considerable interest in using cooperative communications in the next generation of cellular technologies, i.e. WiMAX and LTE, as well as WiFi. This lecture will provide an introduction to these technologies and how they could be incorporated into next generation systems.
This lecture explains the fundamentals and subtleties involved in point-to-point and broadcast transmission of signals from satellite or terrestrial locations. Starting off with the transmitting system and following the signal path through space to the receiving antenna and receiver, the effects of atmospheric loss and receiver noise are analyzed with respect to the signal-to-noise ratio and the ultimate ability of the communication system to recover the originally transmitted signal. An example is given studying the effects of communicating through a geostationary satellite.
Satellite communications have been around for several decades and continues to evolve to service a multitude of users with varying requirements and expectations. Initially satellites were used for direct point-to-point telephone communications. This was an attractive alternative to transoceanic cables. As the technology evolved, it was realized that satellites were a natural topology for broadcast television. While satellite communications remains competitive in the broadcast arena today, is has been relegated to a niche communications market e.g. mobile applications, isolated communities, undeveloped areas, etc. This lecture explanations satellite communications technology and outlines its advantages and limitations. Starting off with the space topology and continuing to discuss various satellite configurations, the lecture discusses the Earth Station segment bringing the remaining pieces of this technology together.
Wireless MIMO (Multiple-Input Multiple-Output) communication exploits phenomena such as multipath propagation to increase data throughput and range rather than attempting to eliminate effects of multipath propagation as traditional SISO (Single-Input Single-Output) communication systems seek to do. The basic theory behind MIMO used in modern high throughput wireless networks and some of its applications, are reviewed. MIMO is the underlying technology for the emerging IEEE 802.11n WLAN standard using multiple antennas and signal processing to more than quadruple the 20-25 Mbps throughput achievable with 802.11g and 802.11a.
This presentation begins with an outline the potential effects of threats posed by acts of terrorism and our national infrastructure, currently vulnerable to weapons of mass destruction. Following this, a brief description will be provided of some of the programs in which engineers and scientists are engaged on a national basis that are designed to defeat or mitigate those threats. Finally, the presentation will discuss the changing role of the Engineer in this new environment and some proposals for the future engagement of the Long Island technical community.
The use of wireless LANs, although not yet ubiquitous, is developing momentum as more and more people look to access corporate Intranets, home networks, and the Internet from mobile wireless platforms. In this lecture, a unique past/present/future perspective on the good and bad of IEEE 802.11 Wireless LANs will be presented. During the session, 802.11’s positioning relative to wireless PANS, and WANS, including Bluetooth and 3G, are discussed. Concepts such as “technology escape-velocity,” and the possibility of 802.11 becoming a technology disrupter for other broadband offerings, are also addressed. In addition, Mr. Willins will look at future services and enhancements coming to next generations 802.11 WLANs. Originally presented at the Things That Think conference held at MIT in May of this year, the presentation spans a wide spectrum of topics, ranging from the technical forethought for hidden terminal resolution, to the proverbial “duct tape” of Wired Equivalent Privacy (WEP).
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2015-11-07 |
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Vice
Chair
Wireless
Communications
Lyubov Renselaer -
Computer Training Center