Series: Integrated Circuits for Communications

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Natasha Simonovski

Series: Integrated Circuits for Communications

Fri, 10/04/2013 - 09:56 — Natasha Simonovski

In this issue of the Integrated Circuits for Communications Series, we continue the theme of integrated circuit design for multi-standard radios. We have selected two papers covering this area, which is drawing significant attention from industry as well as research communities worldwide.

In the past 30 years, wireless technologies have dra- matically penetrated into every aspect of our lives. Today, virtually everyone around the world carries a cell phone or a connectivity device to access multimedia services. As wireless standards diversify, such mobile devices have become increasingly complex in having multiple radios to support multiple standards. Current cell phones typically support six radios, including: cellular, Wi-Fi, Bluetooth, global position system (GPS), FM, and near-field com- munications (NFC). The use case has also become increasingly sophisticated with demands rising to support the concurrent use of multiple services, for instance, being able to use the GPS for navigation while speaking on the phone or browsing on the Internet. Such a concur- rent use scenario requires multiple radios to be on at the same time, which stresses the power consumption as well as cost of the mobile device. While software defined radio (SDR) technologies have been touted for their flex- ibility and configurability to support multiple standards (see the April 2012 issue), concurrent use cases add to the already challenging SDR design the need to be pro- grammable for not just one standard but multiple stan- dards at the same time. 

In past issues of our series (August 2005, August 2006, April 2012, and October 2012), we have seen a clear trend in advances made on circuits implementa- tions for SDR’s. However, the added challenge of sup- porting multiple wireless standards concurrently has not been addressed. In the first paper, entitled “Digital Transmitter Design for Mobile Devices,” the authors

present a digitally intensive multi-standard transmitter design that can be programmed to support the transmis- sion of not only Wi-Fi but also Bluetooth waveforms. Moreover the authors give a broad birds eye view of major transmitter architectures and discuss the key trade-offs that drove them to select the RF digital quadrature architecture for their design, which has achieved a 37 percent drain efficiency at 24.7dBm peak power with a small die area of 0.7mm2 in 40nm comple- mentary metal oxide semiconductor (CMOS) technology. Their chip achieves the error-vector magnitude (EVM) and adjacent channel leakage ratio (ACLR) require- ments for long-term evolution (LTE), IEEE 802.11ac, and Bluetooth enhanced data rate mode.

On the receive side, to support most of the standards today, a SDR is required that can receive a broad spec- trum spanning 500MHz to 3GHz. Conventional SDRs utilize flexible radio-frequency (RF) down conversion followed by Nyquist sampling to digitize an RF signal for reception in the digital domain. More sophisticated SDRs enable the concurrent reception of multiple radio signals compliant with different standards occupying anywhere within the 500MHz to 3GHz. Ultimately, the ability to digitize multi-GHz of spectrum and be able to not only receive predetermined but also unknown chan- nels over a wide spectrum leads to the realization of cognitive radios — the holy grail that we have not yet realized.

To digitize multi-GHz spectrum, an ultra high speed and high dynamic range analog-to-digital converter is nec- essary, which results in an impractical implementation requiring expensive exoteric processing technology, as well as excessive power consumption. However, most of the time, the 3GHz spectrum is unoccupied, i.e. sparse. In this case, when the occupied spectrum is small RF bandwidth, compressive sensing promises an unambiguous recovery of the incoming signals even under significant under-sam- pling. The second paper, entitled “Compressive Samplers for RF Environments,” discusses the application of com- pressive sensing theory to RF signal reception. The author provides an overview of compressive sensing and proposes a non-uniform sampling approach and compares computa- tional complexity, as well as noise penalty with respect to Nyquist sampling for different spectrum occupancy levels. The compressive sampling concept has been demonstrated with a prototype implemented with an Indium Phosphide (InP) front-end together with two commercial off-the-shelf ADCs.

We would like to take this opportunity to thank all the authors and reviewers for their contributions to this Series. Future issues of this series will continue to cover circuit technologies that are enabling new emerging communication systems. If readers are interested in sub- mitting a paper to this Series, please send your paper title and an abstract to any of the Series Editors for consideration. 

 

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