Circuits and Systems for Wireless

Frequency-Division Duplexing (FDD) RF Transceiver

Sameet Ramakrishnan, Lucas Calderin, Antonio Puglielli

The difficulty of building globally compatible wireless devices stems from the myriad of different frequency bands, for example 43 in LTE, which exist across the world, and which can differ greatly even between neighboring countries . While many wideband and configurable radio transceivers have been demonstrated, the limitation is in the implementation of the interference mitigation – particularly suppressing self-interference during simultaneous operation of the transmitter (TX) and the receiver (RX) within the same system during Frequency Division Duplexing (FDD) operating modes. Currently, this isolation is provided by external FBAR or SAW duplexers, which are by their very nature discrete and narrow-band. In practice, a separate, fixed duplexer is used for each cellular band, and if a handset supports multiple bands, multiple duplexers would be used. This work explores the feasibility of fully integrated transceiver architectures with dynamically reconfigurable electronic cancellation for wideband FDD operation.


Wideband TDD Coexistence Front-End

Sharon Xiao, Amanda Pratt

The proliferation of Time-Division Duplexing (TDD) bands have been growing in cellular applications, and thus, there has been renewed interest in enabling TDD coexistence with low cost and high performance. Conventionally, an off-chip T/R switch is employed to isolate the transmit and receive front-ends. However, off-chip components are generally bulky, expensive, and not configurable. In order to support the large number of bands required of modern cellular transceivers, an equally large number of these external components would be needed, which significantly increases system area and cost.

State-of-the-art integrated T/R switches generally have higher loss, which degrades both transmit and receive performance via PA efficiency and LNA noise figure. Furthermore, these switches are generally narrowband, which gives them very limited configurability, and once again, a large number would be needed to support multiple bands, increasing chip area and cost. We propose a novel front-end architecture that enables wideband, integrated TDD coexistence with low overhead and low loss.


eWallpaper: Massive Array of Radios

Antonio Puglielli, Amy Whitcombe, Vladimir Milovanovic

State-of-the-art wireless standards such as 802.11ac and LTE are capable of achieving throughputs very close to the Shannon limit. However, as demand for data increases exponentially, wireless networks have become interference limited, meaning that the available capacity is limited not by the channel, but by the sheer number of devices seeking access. To address this challenge, it is necessary to exploit the spatial structure of the wireless environment. By using multi-user beamforming, base-stations and user terminals can radiate signals in a spatially selective manner. This presents two main benefits. First, several users can simultaneously share the same frequency resources since their signals can be distinguished by their spatial signature. Second, base-stations and user devices can identify the direction of prominent interferers and reject them.

In this project, we are designing an SoC to serve as a common module for a scalable base-station array. We can exploit the large number of elements and the spatial combining capability to design energy-efficient algorithms and hardware. We plan to demonstrate multi-user communications using an array of interconnected, identical chips.


Control Over Wireless

Paul Rigge

The Control over Wireless project’s goal is to develop new wireless architectures to support the high-reliability, low-latency communication necessary for control applications. The targeted applications include current-day critical control applications such as industrial printing, automotive, and smart grid applications, but also future Internet of Things applications as cheap, ubiquitous wireless moves more feedback loops into the home.

This project is supported by an NSF Graduate Research Fellowship and grants CNS-0932410, CNS-1321155, and ECCS-1343398.