Current Research Projects
Please click here for a quick snapshot of our current research.-
Signal Processing with Low Precision ADC : Towards Low Cost Gigabit Wireless Communication
As communication systems scale up in speed and bandwidth, the power consumption and cost of high-precision (e.g., 6-12 bits) analog-to-digital conversion (ADC) becomes the limiting factor in modern receiver architectures based on digital signal processing. In this work, we are considering the effects of lowering the precision of the ADC on the performance of the communication link. The topics under investigation range from the design of DSP algorithms that explicitly take ADC imperfections into account for operations such as synchronization, channel estimation and equalization, to the derivation of information-theoretic limits that provide performance benchmarks for communication with imperfect ADC. Apart from transceiver design for high speed wireless communication, the general framework of signal processing with sloppy ADC could also have other potential applications, such as providing methods for monitoring wide swaths of spectrum for cognitive radio.
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Millimeter-Wave MIMO: Wireless Links at Optical Speeds
The millimeter-wave (mm-wave) MIMO architecture is designed to achieve optical data rates (40 Gbps and higher) over point-to-point wireless links. By allowing high-capacity wireless links to be set up quickly and cost-effectively, mm-wave MIMO has application in communication infrastructure recovery in the case of emergency or natural disaster. Additionally, the architecture allows inexpensive deployment of wireless "bridge" links between optical networks in environments where installation of fiber is difficult or costly (i.e. city centers, mountains, rivers, etc.).
Mm-wave MIMO employs mm-wave spectrum in the E-band (71-95 GHz) to achieve spatial multiplexing gains in line-of-sight environments. The primary signal processing tasks are divided into an efficient two-level hierarchy. Transmit and receive beamforming, constituting the first level, provides high directivity and allows a range on the order of kilometers in adverse weather conditions. The second level consists of spatial equalization which allows parallel transmission of multiple multi-Gigabit-per-second data streams across the link. Operation at these high data rates presents a number of significant design challenges, demanding the use of hybrid analog/digital signal processing algorithms which are co-designed with the hardware. Hardware-oriented mm-wave MIMO research is currently being pursued by the research groups of Professors Mark Rodwell and Patrick Yue of UC Santa Barbara.
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Millimeter Wave WPAN: Cross-Layer Modeling and Multihop Architecture
The 60 GHz band has been allocated worldwide for short range wireless communications because high atmospheric path loss due to oxygen absorption renders it unsuitable for long distance communications. This abundant unlicensed spectrum in the 60 GHz band offers the potential for multiGigabit indoor wireless personal area networking (WPAN). With recent advances in the speed of silicon (CMOS and SiGe) processes, low-cost transceiver realizations in this millimeter (mm) wave band are within reach. However, mm wave communication links are more fragile than those at lower frequencies (e.g., 2.4 or 5 GHz) because of larger propagation losses and reduced diffraction around obstacles. On the other hand, directional antennas that provide directivity gains and reduction in delay spread are far easier to implement at mm-scale wavelengths. We are working on cross-layer modeling methodology and a novel multihop medium access control (MAC) architecture for efficient utilization of the 60 GHz spectrum, taking into account the preceding physical characteristics. Our in-room WPAN architecture constrains every link to be directional for improved power efficiency (due to directivity gains) and simplicity of implementation (due to reduced delay spread). We have developed an elementary diffraction-based model to determine network link connectivity, and have defined a multihop MAC protocol that accounts for directional transmission/reception, procedures for topology discovery and recovery from link blockages.
Figure 1: A living room mm wave WPAN simulation scenario with an access point and wireless terminals.
Figure 2: The graph shown above illustrates the connectivity consistency simulation results for a single hop communication scheme (e.g., IEEE 802.11 MAC Infrastructure mode) and the multihop relay directional MAC.
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