Browsing by Author "Duarte, Melissa"

Now showing 1 - 4 of 4
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    Beamforming in MIMO-OFDM systems: Codebook design for efficient implementation
    (2007) Duarte, Melissa; Sabharwal, Ashutosh
    Quantized feedback in multiple antenna systems has potential to increase throughput and/or reduce probability of outage. In this work, we present a method to generate quantization codebooks tailored for efficient implementation of beamforming-based Multiple-Input Multiple-Output (MIMO) transmissions. The proposed codebooks can reduce computational requirements significantly, making feasible an efficient architecture for a real-time transmit beamforming and receive combining MIMO orthogonal frequency division multiplexing (OFDM) system. Simulation results validate the proposed codebook construction method and architecture.
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    FPGA in Wireless Communications Applications
    (Elsevier, Waltham, MA, 2012-07-12) Amiri, Kiarash; Duarte, Melissa; Cavallaro, Joseph R.; Dick, Chris; Rao, Raghu; Sabharwal, Ashutosh; Center for Multimedia Communication
    In the past decade we have witnessed explosive growth in the wireless communications industry with over 4 billion subscribers worldwide. While first and second generation systems focused on voice communications, third generation networks (3GPP and 3GPP2) embraced code division multiple access (CDMA) and had a strong focus on enabling wireless data services. As we reflect on the rollout of 3G services, the reality is that first generation 3G systems did not entirely fulfill the promise of high-speed transmission, and the rates supported in practice were much lower than those claimed in the standards. Enhanced 3G systems were subsequently deployed to address the deficiencies. However, the data rate capabilities and network architecture of these systems were insufficient to address the insatiable consumer and business sector demand for the nomadic delivery of media and datacentric services to an increasingly rich set of mobile platforms.
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    Full-duplex Wireless: Design, Implementation and Characterization
    (2012) Duarte, Melissa; Sabharwal, Ashutosh
    One of the fundamental assumptions made in the design of wireless networks is that the wireless devices have to be half-duplex, i.e., they cannot simultaneously transmit and receive in the same frequency band. The key deterrent in implementing a full-duplex wireless device, which can simultaneously transmit and receive in the same frequency band, is the large power differential between the self-interference from a device's own transmissions and the signal of interest coming from a distant source. In this thesis, we revisit this basic assumption and propose a full-duplex radio design. The design suppresses the self-interference signal by employing a combination of passive suppression, and active analog and digital cancellation mechanisms. The active cancellations are designed for wideband, multiple subcarrier (OFDM), and multiple antenna (MIMO) wireless communications systems. We then implement our design as a 20 MHz MIMO OFDM system with a 2.4 GHz center frequency, suitable for Wi-Fi systems. We perform extensive over-the-air tests to characterize our implementation. Our main contributions are the following: (a) the average amount of active cancellation increases as the received self-interference power increases and as a result, the rate of a full-duplex link increases as the transmit power of communicating devices increases, (b) applying digital cancellation after analog cancellation can sometimes increase the self-interference and the effectiveness of digital cancellation in a full-duplex system will depend on the performance of the cancellation stages that precede it, (c) our full-duplex device design achieves an average of 85 dB of self-interference cancellation over a 20 MHz bandwidth at 2.4 GHz, which is the best cancellation performance reported to date, (d) our full-duplex device design achieves 30-84% higher ergodic rates than its half-duplex counterpart for received powers in the range of [-75, -60] dBm. As a result, our design is the first one to achieve Wi-Fi ranges; in comparison, no implementation to date has achieved Wi-Fi ranges. Consequently, we have conclusively demonstrated that Wi-Fi full-duplex is practically feasible and hence shown that one of the commonly made assumptions in wireless networks is not fundamental.
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    Physical Layer Algorithm and Hardware Verification of MIMO Relays Using Cooperative Partial Detection
    (IEEE, 2010-03-01) Amiri, Kiarash; Wu, Michael; Duarte, Melissa; Cavallaro, Joseph R.; Center for Multimedia Communication
    Cooperative communication with multi-antenna relays can significantly increase the reliability and speed. However, cooperative MIMO detection would impose considerable complexity overhead onto the relay if a full detect-and-forward (FDF) strategy is employed. In order to address this challenge, we propose a novel cooperative partial detection (CPD) strategy to partition the detection task between the relay and the destination. CPD utilizes the inherent structure of the tree-based sphere detectors, and modifies the tree traversal so that instead of visiting all the levels of the tree, only a subset of the levels, thus a subset of the transmitted streams, are visited. Based on this methodology, the destination combines the source signal and the partial relay signal to perform the detection step. We show, in both simulation and hardware verification on the WARP platform, that using the CPD approach, the relay can avoid the considerable overhead of MIMO detection while helping the source-destination link to improve its performance.