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ABSTRACT: In wireless communications systems that potentially operate in interference, acquisition and temporal alignment of a transmitted signal by a receiver can be the most fragile component of the link. In this paper, synchronization detection in the presence of interference for multiple-input multiple-output (MIMO) communication is discussed. Here, synchronization indicates signal acquisition and timing estimation at the receiver, and is formulated as a binary statistical hypothesis test. Transmit sequences from multiple antennas are received by multiple antennas in noisy environments with spatially correlated noise (interference). Flat-fading and frequency-selective channel models for both the interference and signal of interest are considered. By applying well-known multiple antenna approaches to the MIMO synchronization problem, a number of new synchronization test statistics are introduced. These test statistics are motivated by minimum-mean-square-error (MMSE) beamformers, generalized-likelihood ratio test (GLRT), least-squared (LS) channel estimation, and spatial invariance. Test statistics appropriate for orthogonal-frequency-division-multiplexing (OFDM) systems are considered, including test statistics that take advantage of cyclic prefixes and of pilot sequences within an OFDM symbol. Performances of various test statistics in terms of probability of missing detection for some probability of a false detection are shown to vary by multiple orders of magnitude in the presence of interference.
IEEE Transactions on Signal Processing 04/2010; · 2.63 Impact Factor
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ABSTRACT: We derive several new outer bounds on the capacity of the MIMO Gaussian interference channel. Many of the bounds presented herein are extensions of the work by Etkin et al. (2007) on the single antenna interference channel. These bounds are compared with a Han and Kobayashi achievable rate region and we show the conditions when the achievable rate approaches the outer bound. We also describe the conditions when the outer bounds are concave, thus guaranteeing a computable outer bound.
Signals, Systems and Computers, 2008 42nd Asilomar Conference on; 11/2008
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ABSTRACT: Cooperative diversity systems are wireless communication systems designed to exploit cooperation among users to mitigate the effects of multipath fading. In fairly general conditions, it has been shown that these systems can achieve the diversity order of an equivalent multiple-input multiple-output (MIMO) channel and, if the node geometry permits, virtually the same outage probability can be achieved as that of the equivalent MIMO channel for a wide range of applicable signal-to-noise ratio (SNR). However, much of the prior analysis has been performed under the assumption of perfect timing and frequency offset synchronization. In this paper, we derive the estimation bounds and associated maximum a posteriori estimators for frequency offset estimation in a cooperative communication system. We show the benefit of adaptively tuning the frequency of the relay node in order to reduce estimation error at the destination. We also derive an efficient estimation algorithm, based on the correlation sequence of the data, which has mean squared error close to the Cramer-Rao Bound (CRB).
IEEE Transactions on Signal Processing 09/2008; · 2.63 Impact Factor
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ABSTRACT: The high signal-to-noise ratio capacity of the symmetric MIMO interference channel is characterized as a function of the interference-to-noise ratio. This work is a multiple antenna extension of the degrees of freedom expressions derived by Etkin et al. for the single antenna case. This characterization considers the case where the number of receive antennas is greater than or equal to the number of transmit antennas and shows the number of degrees of freedom available for communication as a function of log(INR)/log(SNR).
Information Sciences and Systems, 2008. CISS 2008. 42nd Annual Conference on; 04/2008
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ABSTRACT: We consider a collaborative communication system consisting of several nodes jointly communicating to a common destination node. Once each node determines the message to send, a space-time code across the sources is used to transmit the signal to the destination. As there may be frequency offsets and unknown frequency selective channels, we assume a training sequence is sent in the preamble to estimate these parameters. In this paper, we derive an algorithm that designs training sequences that minimize the Cramer-Rao Bound for frequency estimation in a frequency-selective environment for a multiple node collaborative communication system.
Signals, Systems and Computers, 2007. ACSSC 2007. Conference Record of the Forty-First Asilomar Conference on; 12/2007
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ABSTRACT: One of the limiting factors in ad hoc wireless mesh networks using traditional physical layer techniques is the inability to transmit and receive at the same frequency simultaneously. As a consequence, careful time-slot or frequency-reuse planning is required. This has adverse network data-rate and latency implications. The focus of this paper is a demonstration of signal processing techniques that enable simultaneous transmission and reception. These techniques employ informed-transmittermultiple-input multiple-output (MIMO) links. A combination of adaptive transmit and receive antenna array approaches is exploited. A number of important types of networking limitations can be resolved given simultaneous transmit and receive technology. The first example is the simultaneous link problem. By employing transmit and receive spatial adaptivity, two links can operate in close proximity using the same frequency at the same time. Another example is the full duplex relay node. Using the same frequency for both links, a given node can simultaneously receive packets from one node while forwarding them to another. For practical systems, two issues dominate performance: channel estimation error, often caused by stale estimates of the channel at the transmitter, and dynamic range limitations of the transmitter and receiver. These issues are investigated. Theoretical, simulated, and experimental results are presented.
Statistical Signal Processing, 2007. SSP '07. IEEE/SP 14th Workshop on; 09/2007
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ABSTRACT: Cooperative diversity systems are wireless communication systems designed to exploit cooperation among users to mitigate the effects of multipath fading. In fairly general conditions, it has been shown that these systems can achieve the diversity order of an equivalent MISO channel and, if the node geometry permits, virtually the same outage probability is achieved as that of the equivalent MISO channel for a wide range of applicable SNR. However, much of the prior analysis has been performed under the assumption of perfect timing and frequency offset synchronization. In this paper, we derive the estimation bounds and associated maximum likelihood estimators for frequency offset estimation in a cooperative communication system. The cooperative nature of the system is utilized to reduce the estimation error with respect to standard (non-cooperative) frequency estimation algorithms. For a worst case frequency offset distribution among the nodes, we show that this estimator is optimal in the sense of estimation error variance.
Distributed Computing Systems Workshops, 2007. ICDCSW '07. 27th International Conference on; 07/2007
