PHY Basics: How OFDM Subcarriers Work

Have you ever wondered just "how" OFDM subcarriers are able to be spaced so tightly together without any guard band in-between? Most Wi-Fi textbooks will simply state that the spacing of the subcarriers allows the harmonics to overlap, thus canceling out any interference.

OFDM subcarrier spacing creates "nulls" canceling out inter-carrier interference (ICI) without the need for guard bands or expensive bandpass filters

OFDM subcarrier spacing creates "nulls" canceling out inter-carrier interference (ICI) without the need for guard bands or expensive bandpass filters

OFDM divides a given channel into many narrower subcarriers. The spacing is such that the subcarriers are orthogonal, so they won’t interfere with one another despite the lack of guard bands between them. This comes about by having the subcarrier spacing equal to the reciprocal of symbol time. All subcarriers have a complete number of sine wave cycles that upon demodulation will sum to zero. 

This tells us that the spacing of the subcarriers is directly related to the useful symbol time (more specifically, the amount of time the transmitter spends performing IFFT). Because of this relationship, the resulting sinc frequency response curves from each subcarrier create signal nulls in the adjacent subcarrier frequencies thus preventing inter-carrier interference (ICI). OFDM is a form of frequency division multiplexing (FDD), which typically requires guard bands between carriers and specialized hardware Continue reading

Wunderlist hooks up with Microsoft’s Sunrise calendaring app & the next thing you know…

Microsoft's 2015 acquisition spree shows no sign of abating: The latest scuttlebutt is that the company has snapped up Germany's 6Wunderkinder to-do list app maker.As I documented in April ("What's behind Microsoft's not-so-crazy acquisition spree?"), Microsoft was off to its fastest acquisition pace ever this year with 4 deals confirmed and 1 widely rumored to have been signed (and in fact, Microsoft recently confirmed the buyout of that 5th company, Surface pen maker N-trig).To read this article in full or to leave a comment, please click here

Report: Microsoft acquires startup behind Wunderlist to-do app

Microsoft has acquired 6Wunderkinder GmbH, a German startup that makes the popular Wunderlist to-do list application, according to a report by the Wall Street Journal.The deal was worth between $100 and $200 million, and is the latest in a string of acquisitions from the Redmond company aimed at bolstering its cross-platform holdings in the mobile productivity space. 6Wunderkinder’s staff will continue to work out of the firm’s Berlin office, but will report to Microsoft’s headquarters in Washington. The report squares with an earlier article from VentureBeat, which said the deal would be valued below $250 million.To read this article in full or to leave a comment, please click here

Report: Microsoft acquires startup behind Wunderlist to-do app

Microsoft has acquired 6Wunderkinder GmbH, a German startup that makes the popular Wunderlist to-do list application, according to a report by the Wall Street Journal.The deal was worth between $100 and $200 million, and is the latest in a string of acquisitions from the Redmond company aimed at bolstering its cross-platform holdings in the mobile productivity space. 6Wunderkinder’s staff will continue to work out of the firm’s Berlin office, but will report to Microsoft’s headquarters in Washington. The report squares with an earlier article from VentureBeat, which said the deal would be valued below $250 million.To read this article in full or to leave a comment, please click here

SanDisk enters portable drive market with high-speed SSDs

SanDisk, known for thumb drives, memory cards and internal SSD, has announced its first line-up of pocket-sized, high-capacity external drives.The new line of drives includes four products of varying size, ranging in capacity from 120GB to 1.9TB. The new line includes the Extreme 900 Portable SSD, which uses the new, reversible USB Type-C connector with throughput up to 850MB/s.All of the drives come native with SanDisk SecureAccess software, which uses 128-bit AES encryption to password protect data.To read this article in full or to leave a comment, please click here

25 burning questions about Windows Server 2003 end of support

You know it well by now: Windows Server 2003 support is ending July 14, 2015. If you're one of the (far too) many still running WS2003, it's time to arm yourself with your action plan because what you don't know can hurt you.ALSO ON NETWORK WORLD: What if Windows went open source tomorrow? With help from the IDG Answers community, we collected some of most burning questions enterprises and individuals have about WS2003 end of support -- how it will affect them, how to prepare, what the options are. If you have advice you'd like to share, or lingering questions, add a comment below or join the discussion on IDG Answers.To read this article in full or to leave a comment, please click here

IDG Contributor Network: Backup and Restore on the Cisco ASA 9.3

In a recent blog post, I examined some of the new features available in the Cisco Adaptive Security Appliance (ASA) 9.3 code and promised to cover some of these here at the blog. With that said, let's examine the Backup and Restore functionality that is now built in to these devices. The first question we will tackle is what exactly is backup up through this process. The answer is just about everything you could want on your system! Here is the complete list: The Running-configuration The Startup-configuration All security images, including the Cisco Secure Desktop and Host Scan images, Cisco Secure Desktop and Host Scan settings, AnyConnect (SVC) client images and profiles, and AnyConnect (SVC) customizations and transforms Identity certificates (includes RSA key pairs tied to identity certificates; excludes standalone keys) VPN pre-shared keys SSL VPN configurations Application Profile Custom Framework (APCF) Bookmarks Customizations Dynamic Access Policy (DAP) Plug-ins Pre-fill scripts for connection profiles Proxy Auto-config Translation table Web content Version information So you have just made some configuration changes and you are ready to backup your device. Here are some things to keep in mind:To read this article in full or to leave a comment, please click here

IDG Contributor Network: Projecting the Internet of Things’ massive potential impact on business

Often, when we hear about Internet of Things (IoT), we think of it in terms of consumer-oriented scenarios—home security, switching lights on, fitness bands, and so on.But in fact, the IoT has room to completely transform business too. Telematics isn't just consumer-oriented.Gartner analyst Daryl Plummer presented a webinar on digital innovation recently, and in it he provided a synopsis on where he thinks IoT and business is headed.To read this article in full or to leave a comment, please click here

CA names Xbox cofounder its new CTO

Xbox cofounder Otto Berkes may have spent the bulk of his recent years focusing on consumer technology, but his next career move will be set squarely in the enterprise arena, as CA Technologies on Monday announced that it recruited him to serve as its next CTO.Most recently, Berkes was CTO at HBO, where he was responsible for the development of HBO Go as well as all of the company’s technology efforts including media production, internal business systems and technology operations.Before that, Berkes—who has been awarded seven patents and is one of the four original founders of Xbox—spent 18 years at Microsoft, where he held a number of senior-level positions including senior software developer, partner-level architect and general manager.To read this article in full or to leave a comment, please click here

BlackBerry settlement allows Typo keyboards for iPads, not iPhones

BlackBerry has reached a settlement with Typo Innovations, which made an accessory keyboard for iPhones that the handset maker said infringed its patents.Under the settlement announced Monday, Typo, which was co-founded by “American Idol” host Ryan Seacrest, is barred from selling keyboards for devices with screen sizes smaller than 7.9 inches.BlackBerry sued Typo in 2014 after the company released a keyboard that fit the iPhone 5 or 5S like a protective case; BlackBerry claimed the keyboard copied those found on its own handsets. The keyboard is one of the differentiating features that has made BlackBerry loyalists cling to their old-school smartphones.To read this article in full or to leave a comment, please click here

BlackBerry settlement allows Typo keyboards for iPads, not iPhones

BlackBerry has reached a settlement with Typo Innovations, which made an accessory keyboard for iPhones that the handset maker said infringed its patents.Under the settlement announced Monday, Typo, which was co-founded by “American Idol” host Ryan Seacrest, is barred from selling keyboards for devices with screen sizes smaller than 7.9 inches.BlackBerry sued Typo in 2014 after the company released a keyboard that fit the iPhone 5 or 5S like a protective case; BlackBerry claimed the keyboard copied those found on its own handsets. The keyboard is one of the differentiating features that has made BlackBerry loyalists cling to their old-school smartphones.To read this article in full or to leave a comment, please click here

Pure says users can upgrade the same all-flash array for a decade

Enterprise storage is a long-term bet. Pure Storage, a growing maker of all-flash arrays, is reshuffling the deck on that gamble in a way that might save IT departments time and money.Pure’s plan is to let customers keep the same system for a decade, upgrading various components as improved versions come out but never having to migrate the data from an older array to a new one. For some organizations, this could eliminate an expensive and time-consuming effort every few years.The elements of the new approach have been coming together for a while. But the company formally introduced the strategy and gave it a name—Evergreen Storage—as it unveiled its fourth-generation product on Monday. Evergreen Storage applies to all generations of Pure hardware already shipped as well as versions yet to come.To read this article in full or to leave a comment, please click here

Nokia wants to build data centers for mobile operators

Nokia wants to help mobile network operators launch new services and cut their costs with a new range of servers, switches and storage they can use to virtualize their networks.Enterprises have already adopted virtualization and cloud-based IT infrastructures, and now telecommunications operators are looking at doing the same thing. Meanwhile equipment vendors like Nokia are increasingly offering operators the hardware and software to provide telephony, messaging and mobile broadband as virtualized services.Telecommunications operators instigated the move away from dedicated, proprietary equipment to virtualized hardware. A group including AT&T, Verizon, China Mobile, Orange and Deutsche Telekom proposed a concept called NFV (Network Functions Virtualization), which is now being standardized by the European Telecommunications Standards Institute.To read this article in full or to leave a comment, please click here

Google’s new privacy settings page aims to gives users more control

Google has launched a centralized hub that lets users manage the privacy and security controls of all its services, and introduced a site with information about these topics.The hub, called My Account, is not the first effort from Google to centralize settings: in 2009, it introduced a dashboard to let users control settings on most services on one page.On My Account, people can control settings for Search, Maps, YouTube, Gmail and other products in one place, Google said in a blog post on Monday.To read this article in full or to leave a comment, please click here

Facebook will send encrypted emails as users add PGP key to profile

Some Facebook users should soon be able to receive encrypted emails from the social networking site if they add PGP public keys to their profiles. Facebook called the PGP feature “experimental” and said it is slowly rolling it out, although a timeline wasn’t provided. The PGP key details will be added to the “contact and basic info section” of a person’s profile under “contact information.” Facebook sends messages to private email accounts to inform users when they have a private message or friend request, for example. It currently uses TLS to establish secure connections to a person’s email provider, but this won’t keep the details of an email private from prying eyes.To read this article in full or to leave a comment, please click here

1 … 3,376 3,377 3,378 3,379 3,380 … 3,756