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JJD: What technology trend is having the biggest impact on the communications market today?

AE: Connectivity is still the name of the game. The development of very-low-power, energy-efficient wireless devices will enable another 10 to 100 billion devices to be connected to the Internet—including machine-to-machine (M2M) connections and the “Internet of Things” (IoT). All those devices connecting with the network will cause bottlenecks. We believe our WAve Modulation (WAM) helps here, as there will be a need for extremely high-speed wireless-backhaul links to get around right-of-way issues. Such connectivity also will be aided by the development of good, inexpensive infrastructure to connect homes and offices to the Internet backbone at speeds far exceeding what we see today. In addition, development of a robust mobile (cellular) wireless infrastructure will enable us to stay connected any time. Solutions based on small cells will be used to improve access reach while solutions like WAM will help by taking advantage of the increased signal-to-noise ratio (SNR).

JJD: What are some of the big application-layer shifts driving new needs at layer 1?

AE: First, more processing is happening "in the cloud" (i.e., at some server farm [Amazon EC2, Google, etc.]). There is an increased need for high-speed and low-latency connections between fixed and mobile devices to the Internet backbone. We're relying on these new "cloud-based" services all the time—for navigation, processing data from sensors on our body (for health and fitness monitoring), and posting, consuming, and searching for content. Many more devices need a connection to the Internet backbone and services that ride on top of them. Whether they are smart watches, wristbands, or sensors that will measure our pulse or footsteps; their data must be aggregated somewhere else. And don’t forget video, which is the new still photo. We will be capturing a lot more visual data—much of which is of limited temporal value. In five years, we'll create and discard more content in a day than we now create and save in one year. Much of that content will never be seen by a human being, but will automatically be processed and filtered. All this means that we'll need more bandwidth--both for access connections and backbone and backhaul connections. 

JJD: From a communication designer’s viewpoint, what is the biggest challenge in meeting design demands?Amir Eliaz

AE: First, we need to ensure that the high-speed pipes we're building into mobile devices don't drain the batteries or render the device too hot to hold. These are big problems. Wireless interfaces now are a top consumer of power (and energy per processed bit) in most mobile devices. Second, we need to ensure sufficient access capacity to users in dense urban areas. We also need to provide sufficient backhaul capacity to the core network. Meanwhile, costs need to keep dropping.

JJD: From a communications technology standpoint, what must be done to meet the demands for “big data?”

AE: Excellent question. We need both very big backhaul and access pipes for mobile devices to provide the high-speed burst capabilities for opportunistically generated and consumed video content. They also will support "real-time" cloud-based services using input from these devices. We don't have a lot more "quality spectrum," so we need solutions that maximize spectrum utilization.

JJD: What major challenges do you face when designing communication systems for millimeter-wave applications?

AE: There are a number of them. Antenna and feed design is a massive challenge in some devices. Take a look at an Apple iPhone 5S and marvel at all that aluminum. Somewhere, an antenna array would need to be exposed to the world. To achieve the highest data rates, large antenna-array gains would be required to meet the link-budget constraints for reasonable distances (more than a couple of meters). These channels change very, very rapidly. So, sophisticated beamforming algorithms are required. In addition, a lot of processing power is needed to update the arrays. In mobile-backhaul and small-cell applications, the radio is very nonlinear. These nonlinearities cause the radio to suffer from amplifier compression and frequency-source phase noise, which limit spectral efficiency. Current systems are operating at low spectral efficiency because of the amount of available spectrum, which is not ideal. In the future, however, high-order modulation should be used as spectrum is less available and nonlinearity becomes a critical issue.

JD: What are the requirements for enabling higher-constellation quadrature-amplitude-modulation (QAM) systems?

AE: For backhaul systems, the challenges are primarily nonlinearities in the channel--both phase noise at the transmitter/ receiver, power-amplifier (PA) compressive nonlinearities, and phase noise. These limit the maximum spectral efficiency for QAM today. For mobile wireless systems, we see the same challenges--plus substantial co-channel interference.

JJD: How are communications engineers handling the new requirements of LTE-A with multiple-input multiple-output (MIMO) and carrier aggregation?

AE: MIMO suffers the problem of increased complexity at the receiver--particularly in frequency reuse 1 systems, in which there is substantial co-channel interference at the cell boundaries (the majority of the area). Apparently, carrier aggregation provides higher per-user throughput, but it requires clever scheduling to avoid higher latency for some users. It would be beneficial to also increase spectral efficiency for a single spatial channel.

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