Now showing items 1-20 of 69

    • Achievable Diversity and Multiplexing in Multiple Antenna Systems with Quantized Power Control 

      Khoshnevis, Ahmad; Sabharwal, Ashutosh (2005-05-01)
      We consider a multiple antenna system with finite rate feedback, in which the quantized channel state information at the transmitter is used solely for temporal power control. We show that similar to systems without feedback, ...
    • Achievable Rates for Arbitrary Network Topologies with â Cheapâ Nodes 

      Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam (2003-05-01)
      In this paper, we derive achievable rates for arbitrary network topologies consisting of â cheapâ nodes. A node is labeled â cheapâ if its radio can only operate in TDD mode when transmitting and receiving in the ...
    • Analysis of Decision-Feedback Based Broadband OFDM Systems 

      de Baynast, Alexandre; Sabharwal, Ashutosh; Aazhang, Behnaam (2005-11-01)
      In wireless communications, about 25% of the bandwidth is dedicated to training symbols for channel estimation. By using a semi-blind approach, the training sequence length can be reduced while improving performance. The ...
    • Antenna Packing in Low Power Systems: Communication Limits and Array Design 

      Muharemovic, Tarik; Sabharwal, Ashutosh; Aazhang, Behnaam (2008)
      In this paper, we study design of transceiver antenna arrays and its impact on spectral efficiency of low-power systems. Our primary motivation is construction of practical and portable multi-antenna configurations with a ...
    • An Approach to Capacity Analysis of Coarsely Coordinated Low Power Multiple Access Systems 

      Muharemovic, Tarik; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-07-01)
      We consider multiaccess problem in low power systems, where we allow each user to select its own data rate and transmit power locally and independently from other users. Here, every user has a set of low power codebooks, ...
    • Architectures for Cognitive Radio Testbeds and Demonstrators – An Overview 

      Gustafsson, Oscar; Amiri, Kiarash; Andersson, Dennis; Blad, Anton; Bonner, Christian; Cavallaro, Joseph R.; Declerck, Jeroen; Dejonghe, Antoine; Eliardsson, Patrik; Glasse, Miguel; Hayar, Aawatif; Hollevoet, Lieven; Hunter, Chris; Joshi, Madhura; Kaltenberger, Florian; Knopp, Raymond; Le, Khanh; Miljanic, Zoran; Murphy, Patrick; Naessens, Frederik; Nikaein, Navid; Nussbaum, Dominique; Pacalet, Renaud; Raghavan, Praveen; Sabharwal, Ashutosh; Sarode, Onkar; Spasojevic, Predrag; Sun, Yang; Tullberg, Hugo M.; Vander Aa, Tom; Van der Perre, Liesbet; Wetterwald, Michelle; Wu, Michael (2010-06-01)
      Wireless communication standards are developed at an ever-increasing rate of pace, and significant amounts of effort is put into research for new communication methods and concepts. On the physical layer, such topics include ...
    • Beamformer Design with Feedback Rate Constraints : Criteria and Constructions 

      Mukkavilli, Krishna Kiran; Sabharwal, Ashutosh; Erkip, Elza; Aazhang, Behnaam (2003-07-20)
      In this work, we provide a geometrical framework for the analysis and design of beamformer codebooks with finite number of beamformer vectors. We present a design criterion for good beamfomer codebooks and show the equivalence ...
    • Bounds on Achievable Rates for General Multi-terminal Networks with Practical Constraints 

      Khojastepour, Mohammad; Aazhang, Behnaam; Sabharwal, Ashutosh (2003-04-20)
      We consider the problem of communication in a general multi-terminal network where each node of the network is a potential sender or receiver (or both) but it cannot do both functions together. The motivation for this ...
    • Broadcast Space-Time Coding 

      Memarzadeh, Mahsa; Sabharwal, Ashutosh; Aazhang, Behnaam (2001-08-20)
      In this paper, we study transmission techniques for broadcast channels with a single transmitter and multiple receivers. The transmitter is assumed to be equipped with multiple antennas. Further, each receiver is interested ...
    • Channel Estimation for Multirate DS-CDMA Systems 

      Sabharwal, Ashutosh; Mitra, Urbashi; Bhashyam, Srikrishna (2000-11-20)
      The problem of channel estimation for multiple data rate Direct-Sequence Code-Division Multiple-Acess (DS-CDMA) systems is addressed. The derived algorithms are suitable for both variable chipping rate and/or variable ...
    • Constellations for Imperfect Channel State Information at the Receiver 

      Borran, Mohammad Jaber; Sabharwal, Ashutosh; Aazhang, Behnaam (2002-10-20)
      We consider the problem of digital communication in a Rayleigh flat fading environment using a multiple antenna system. We assume that the transmitter doesn't know the channel coefficients, and that the receiver has only ...
    • COOPERATIVE COMMUNICATIONS: Fundamental Limits and Practical Implementation 

      Chakrabarti, Arnab; Sabharwal, Ashutosh; Aazhang, Behnaam (2006-01-01)
      This chapter summarizes theoretically achievable gains and the construction of practical codes for user-cooperation. Most of these results relate to the relay channel, which is a three-terminal channel that captures the ...
    • Cut-set Theorems for Multi-state Networks 

      Khojastepour, Mohammad; Aazhang, Behnaam; Sabharwal, Ashutosh (2003-10-01)
      We derive new cut-set bounds on the achievable rates in a general multi-terminal network with finite number of states. Multiple states are common in communication networks in the form of multiple channel and nodes' states. ...
    • Data Collection by a Mobile Observer in a Single-hop Sensor Network 

      Chakrabarti, Arnab; Sabharwal, Ashutosh; Aazhang, Behnaam (2005-01-15)
      In this paper, we demonstrate significant reduction in communication power by using a mobile observer to collect data from a wireless single-hop network of static sensors. The key challenge in using a mobile observer is ...
    • Delay and Rate Constrained Transmission Policies over Wireless Channels 

      Rajan, Dinesh; Sabharwal, Ashutosh; Aazhang, Behnaam (2001-11-20)
      In this paper, we study delay and rate-constrained transmission of bursty traffic over wireless channels. We characterize the minimum power requirements via bounds for both single user and multiuser downlink problems, using ...
    • Delay bounded packet scheduling of bursty traffic over wireless channels 

      Rajan, Dinesh; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-01-01)
      In this paper, we study minimal power transmission of bursty sources over wireless channels with constraints on mean queuing delay. The power minimizing schedulers adapt power and rate of transmission based on the queue ...
    • Delay-constrained Scheduling: Power Efficiency, Filter Design, and Bounds 

      Khojastepour, Mohammad; Sabharwal, Ashutosh (2004-03-01)
      In this paper, packet scheduling with maximum delay constraints is considered with the objective to minimize average transmit power over Gaussian channels. The main emphasis is on deriving robust schedulers which do ...
    • Design of Multiple Antenna Coding Schemes with Channel Feedback 

      Mukkavilli, Krishna Kiran; Sabharwal, Ashutosh; Aazhang, Behnaam (2001-11-20)
      In this paper, we derive multiple antenna transmission strategies in the presence of limited channel information at the transmitter and the receiver. In particular, we look at the cases of complete channel information, ...
    • Design of WARP: A Wireless Open-Access Research Platform 

      Murphy, Patrick; Sabharwal, Ashutosh; Aazhang, Behnaam (2006-09-01)
      This paper presents the design of WARP, a custom platform for research in advanced wireless algorithms and applications. The platform consists of both custom hardware and FPGA implementations of key communications blocks. ...
    • DistancePPG: Robust non-contact vital signs monitoring using a camera 

      Kumar, Mayank; Veeraraghavan, Ashok; Sabharwal, Ashutosh (2015)
      Vital signs such as pulse rate and breathing rate are currently measured using contact probes. But, non-contact methods for measuring vital signs are desirable both in hospital settings (e.g. in NICU) and for ubiquitous ...