R. Annavajjala

Mitsubishi Electric Research Laboratories, Cambridge, Massachusetts, United States

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Publications (54)54.18 Total impact

  • Manesh A · Chandra Murthy · Ramesh Annavajjala
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    ABSTRACT: This paper studies the design and analysis of a pilot-assisted physical layer data fusion technique known as Distributed Co-Phasing (DCP). In this two-phase scheme, sensors first estimate the channel to the fusion center (FC) using pilot symbols sent by the latter; and then they simultaneously transmit their common data symbols by pre-rotating them by the estimated channel phase, thereby achieving physical layer data fusion. First, by analyzing the symmetric mutual information of the system, it is shown that the use of higher order constellations can significantly improve the throughput performance of DCP in comparison with binary signaling considered heretofore. Using a higher order constellation in the DCP setting requires the estimation of the composite DCP channel at the FC for data decoding. To this end, two blind algorithms are proposed: 1) power method, and 2) modified K-means algorithm. The latter algorithm is shown to be computationally efficient and converges significantly faster than the conventional K-means algorithm. Analytical expressions for the probability of error are derived, and it is found that even at moderate to low SNRs, the proposed modified K-means algorithm achieves a probability of error comparable to that achievable with perfect channel estimate at the FC, while requiring no pilot symbols to be transmitted from the sensor nodes. Also analyzed is the problem of signal corruption due to imperfect DCP, and constellation shaping to minimize the probability of signal corruption is proposed and analyzed. The analysis is validated and the promising performance of DCP for energy-efficient physical layer data fusion is illustrated using Monte Carlo simulations.
    IEEE Transactions on Signal Processing 01/2015; DOI:10.1109/TSP.2015.2442954 · 3.20 Impact Factor
  • A. Manesh · C.R. Murthy · R. Annavajjala
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    ABSTRACT: In this paper, we design and analyze pilot-assisted Distributed Co-Phasing (DCP) schemes for information fusion in a wireless sensor network. First, using a cutoff rate analysis, we show that higher order constellations significantly improve the throughput performance of DCP in comparison with the binary constellation considered in past work. However, using a higher order constellation in the DCP setting requires estimation of the composite channel from the sensors at the Fusion Center (FC), which is not available in current DCP schemes. We propose two blind algorithms for channel estimation, namely, a power method and a modified K-means algorithm. In particular, the latter is computationally efficient and converges significantly faster and more accurately than the conventional K-means algorithm. We derive closed-form expressions for the probability of symbol error and study the performance of DCP both analytically and through simulations. Our simulation results show that even at moderate to low SNRs, the modified K-means algorithm achieves a probability of error comparable to that achievable with a perfect channel estimate at the FC. The proposed DCP and blind channel estimation schemes are thus a promising technique for energy-efficient data fusion in wireless sensor networks.
    Communications (ICC), 2013 IEEE International Conference on; 01/2013
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    ABSTRACT: We propose a low-complexity turbo equalizer consisting of a sliding window MAP estimator, and a low overhead, small block-size SISO LDPC decoder. Simulations show that the proposed turbo equalizer offers up to 5dB gain in Q-factor over existing sliding window detector in a nonlinear fiber channel over 5,000km.
    Optical Fiber Communication Conference and Exposition (OFC/NFOEC), 2012 and the National Fiber Optic Engineers Conference; 03/2012
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    Liangbin Li · R. Annavajjala · T. Koike-Akino · P. Orlik
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    ABSTRACT: Orthogonal frequency division multiplexing (OFDM) systems are vulnerable to narrow-band jamming signals. We jointly tackle two problems: channel estimation in the presence of unknown interference, and decoding with imperfect channel knowledge. In this paper, we propose robust, yet simple, receiver algorithms consisting of both channel estimation and information decoding. The receiver conducts threshold tests to detect interference followed by pilot erasure and channel estimation. Then, channel estimation error and unknown interference statistics are dealt with by the robust log-likelihood ratio (LLR) calculations for soft iterative decoding. The proposed receiver algorithm does not require any statistical knowledge of interference and its complexity is linear against the length of codewords. Simulation results show that the bit-error-rate (BER) performance of the proposed system is only 2~3 dB away from a genie system where channel information and interference parameters are perfectly known. We also demonstrate that soft decision feedback from a decoder to enhance channel estimation achieves additional 0.5 ~ 1dB improvement.
    MILITARY COMMUNICATIONS CONFERENCE, 2012 - MILCOM 2012; 01/2012
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    Wei Shi · R. Annavajjala · P.V. Orlik · A.F. Molisch · M. Ochiai · A. Taira
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    ABSTRACT: Due to the fine delay resolution in ultra-wideband (UWB) wireless propagation channels, a large number of multipath components (MPC) can be resolved; and the first arriving MPC might not be the strongest one. This makes time-of-arrival (ToA) estimation, which essentially depends on determining the arrival time of the first MPC, highly challenging. In this paper, we consider non-coherent ToA estimation given a number of measurement trials, at moderate sampling rate and in the absence of knowledge of pulse shape. The proposed ToA estimation is based on detecting the presence of a signal in a moving time delay window, by using the largest eigenvalue of the sample covariance matrix of the signal in the window as the test statistic. We show that energy detection can be viewed as a special case of the eigenvalue detection. Max-eigenvalue detection (MED) generally has superior performance, due to the following reasons: 1) MED collects less noise, namely only the noise contained in the signal space, and 2) if multiple channel taps fall into the time window, the MED detector can collect energy from all of them. Simulation results confirm that MED outperforms the energy detection in IEEE 802.15.3a and 802.15.4a channels. Finally, the selection of the threshold of the MED is studied both by simulations and by random matrix theory.
    Communications (ICC), 2012 IEEE International Conference on; 01/2012
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    K.V.K. Chaythanya · Ramesh Annavajjala · C.R. Murthy
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    ABSTRACT: This paper compares and analyzes the performance of distributed cophasing techniques for uplink transmission over wireless sensor networks. We focus on a time-division duplexing approach, and exploit the channel reciprocity to reduce the channel feedback requirement. We consider periodic broadcast of known pilot symbols by the fusion center (FC), and maximum likelihood estimation of the channel by the sensor nodes for the subsequent uplink cophasing transmission. We assume carrier and phase synchronization across the participating nodes for analytical tractability. We study binary signaling over frequency-flat fading channels, and quantify the system performance such as the expected gains in the received signal-to-noise ratio (SNR) and the average probability of error at the FC, as a function of the number of sensor nodes and the pilot overhead. Our results show that a modest amount of accumulated pilot SNR is sufficient to realize a large fraction of the maximum possible beamforming gain. We also investigate the performance gains obtained by censoring transmission at the sensors based on the estimated channel state, and the benefits obtained by using maximum ratio transmission (MRT) and truncated channel inversion (TCI) at the sensors in addition to cophasing transmission. Simulation results corroborate the theoretical expressions and show the relative performance benefits offered by the various schemes.
    IEEE Transactions on Signal Processing 09/2011; DOI:10.1109/TSP.2011.2145374 · 3.20 Impact Factor
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    Wei Liu · Chunjie Duan · Yige Wang · Toshiaki Koike-Akino · Ramesh Annavajjala · Jinyun Zhang
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    ABSTRACT: We discuss a secure wireless communication scheme, focusing on designing two major components: the key generation and the coding scheme. To achieve high key matching rate, we propose a feed-forward and feed-back quantization. The proposed scheme offers 1 dB improvement over the best known schemes. We also propose a universal quantization scheme with feed-forward/feed-back and show that its performance is the same as, or better than the other schemes which require prior distribution information. For rate-adaptive coding, we propose the use of rateless codes. Our evaluations show that the rateless code can offer significant performance gain over a low-density parity-check (LDPC) code. Moreover, we implement a soft input rateless decoder which offers additional gains. The overall security performance of our design based on these two components significantly outperforms existing designs.
    International Conference on Sensor Technologies and Applications; 08/2011
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    R. Annavajjala · P.V. Orlik · Jinyun Zhang
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    ABSTRACT: For orthogonal frequency-division multiplexing (OFDM) based wireless systems, a resource block (RB) in a two-dimensional time-frequency plane is defined as a data block spanned by a number of consecutive OFDM symbols over a number of consecutive subcarriers. Traditionally, RBs contain modulation symbols for data transmission and pilot symbols for channel estimation. In this paper, we present a novel approach to RB designs for OFDM systems with multiple antennas at the transmitter and the receiver (i.e., MIMO-OFDM). The proposed approach, termed resource block embedding, does not require explicit pilot symbols to estimate the channel at the receiver, and hence reduces the channel estimation overhead significantly. We describe, in detail, the encoding and decoding algorithms for our proposed embedded resource blocks (ERB) for single-user single-antenna transmission, two transmitter antenna Alamouti code, four transmitter antenna stacked Alamouti code, and multi-stream spatial multiplexing. We also outline construction of ERBs for multi-user MIMO systems.
    Broadband Multimedia Systems and Broadcasting (BMSB), 2011 IEEE International Symposium on; 07/2011
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    ABSTRACT: We develop a recursive least-squares (RLS) algorithm which employs L<sub>1</sub>-L<sub>q</sub> regularized sparse regressions to estimate a sparse channel matrix in frequency-and-time selective fading for multi-input multi-output (MIMO) wireless communications. We propose an improved sparse RLS by using an order extension technique for rapid fading channels. Simulation results demonstrate that the proposed sparse RLS algorithm offers a significant improvement over the conventional RLS algorithm.
    Proceedings of IEEE International Conference on Communications, ICC 2011, Kyoto, Japan, 5-9 June, 2011; 06/2011
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    R. Annavajjala · P.V. Orlik
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    ABSTRACT: It is well-known that for single-input and single-output (SISO) narrow-band transmission on frequency-flat fading channels, uncoded communication with only receiver channel state information (Rx-CSI) leads to extremely poor reliability performance whereas transmitter CSI (Tx-CSI) allows us approach the reliability of an additive white Gaussian noise (AWGN) channel via power control. In this paper, we propose a novel approach to achieve reliability close to the AWGN channel for uncoded transmissions on SISO frequency-flat Rayleigh fading channels without Tx-CSI. Our approach employs pseudo-random phase precoding (PRPP) of modulation symbols prior to temporal multiplexing, and joint-detection at the receiver that has polynomial complexity in the precoder size. With a precoder size of 400 binary symbols, we demonstrate that the proposed system achieves performance within 0.1 dB of the AWGN channel at a bit error rate of 10<sup>-5</sup>, and is also robust to fading correlation and channel estimation errors. Furthermore, we present extensions to multiple-user multiple-input and multiple-output (MU-MIMO) systems and wideband transmission schemes such as orthogonal frequency-division multiplexing (OFDM) and single-carrier frequency-domain multiple access (SC-FDMA) systems. We show, through extensive simulations, that i) with an 8-by-8 MIMO system per-stream AWGN channel reliability is achieved with 8 spatial streams and 50 channel uses, ii) for a 5 user multiple-access channel with one antenna per user and 5 antennas at the receiver, 80 channel uses eliminates fading and interference completely while simultaneously providing a power gain of approximately 6.9 dB, and iii) for OFDM and SC-FDMA systems with single antenna at the transmitter and two antennas at the receiver, within 0.1 and 0.3 dB of the matched-filter bound performance is achieved with a precoder size of 96 and 400 symbols, respectively.
    Information Theory and Applications Workshop (ITA), 2011; 03/2011
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    A. Maaref · R. Annavajjala · Jinyun Zhang
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    ABSTRACT: In this paper, a multi-antenna two-way relaying protocol is proposed whereby two source nodes wishing to exchange information via a relay node additionally send private messages intended solely for the relay. In particular, we investigate the performance of this bidirectional relaying protocol over fading channels when the relay and source nodes are equipped with multiple antennas thus enabling them to leverage diversity and/or multiplexing gains. Specifically, provided enough antennas are available at the relay, the latter may opt for a demodulate-and-forward approach whereby it demodulates all incoming streams before broadcasting solely the messages to be exchanged between the source nodes or it may opt for a generalized analog network coding approach whereby it only demodulates the private messages destined for the relay's own sake while treating the messages to be exchanged between the source nodes as colored noise, subtracting the demodulated information from the overall received signal and then broadcasting the remaining part of the received signal. We compare how the two approaches fare when coupled with different multiple-input multiple-output (MIMO) detection techniques thus striking suitable tradeoffs between performance and implementation complexity for the generalized multi-antenna two-way relaying channel under consideration.
    Consumer Communications and Networking Conference (CCNC), 2011 IEEE; 02/2011
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    Amine Maaref · Ramesh Annavajjala
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    ABSTRACT: This letter provides a new outlook at the Gamma distribution and its involvement in the performance analysis of digital communications over wireless fading channels. Whereas the Gamma distribution is usually regarded as a two-parameter distribution with a scale and shape factors that are deterministic parameters, we investigate the implications and insight that can be drawn from considering a Gamma variate with a random shape factor. Applications of such a distribution in the context of information transmission over a wireless fading channel are provided and novel average symbol error probability (SEP) expressions for single and multi-channel reception are derived involving the Laplace transform of the new distribution. We analytically prove and verify via numerical simulations that the average SEP results induced by the random shape parameter are lower bounded by those obtained using a deterministic fading severity whose value equals the expected value of the random shape parameter.
    IEEE Communications Letters 01/2011; 14(12-14):1146 - 1148. DOI:10.1109/LCOMM.2010.102810.101632 · 1.46 Impact Factor
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    ABSTRACT: In a multiple-input multiple-output (MIMO) system, cross-polarized antenna selection yields significant reduction in cost and hardware size. However, actual benefits of the technique are dependent on the propagation characteristics including chan- nel polarization. To accurately characterize the target 2 GHz-band MIMO channels, the authors conduct 2 GHz cross-polarized chan- nel measurement campaigns. Based on the measured data, novel channel models specifically for the 2 GHz bands are established. In addition, we evaluate the performance improvement obtained with cross-polarized antenna selection using the channel models. Simulation results reveal that antenna selection is particularly useful in the low SNR regime, and that the system capacity at cell edges can be increased up to 13%. I. Introduction Multiple-input multiple-output (MIMO) technology is a promising technique to achieve higher capacity in wireless communications. However, MIMO transmitter/receiver suffers from higher cost and larger hardware size because it requires multiple antennas and radio frequency (RF) circuits. Antenna selection enables us to overcome this obstacle because the required number of RF circuits can be reduced to the number of selected active antennas. Also, cross-polarized antennas can be implemented in a much confined space compared to identically polarized antennas. A cross-polarized antenna selection scheme incorporating these two techniques therefore is expected to lead to significant reduction in cost and hardware size without sacrificing the advantages of the MIMO systems. On the other hand, effective benefits of these techniques are dependent on the propagation environment. Channel char- acterization including polarization in actual environments is particularly of importance. WINNER (1), which is a channel model extensively used for examining MIMO systems, takes into account polarization. Since it supports 2-6 GHz bands, its parameters were not specifically derived for the 2 GHz bands, which are currently employed in various cellular systems. In particular, cross polarization discrimination (XPD), which is well-known as a key factor determining the cross-polarized channel characteristic and has been extensively examined in the past channel measurement campaigns (2), should be verified for fair evaluation of the cross-polarized antenna selection scheme. In this work, to accurately characterize the 2 GHz-band MIMO channels, the authors conduct 2 GHz cross-polarized channel measurement campaigns. Based on the measured data, novel channel models specific to 2 GHz bands are established. Finally, we evaluate the effect of the cross-polarized antenna selection technique over the channel models. Hereafter, we define Ntx and Nrx as the number of trans- mit (TX) antennas and the number of receive (RX) anten- RX antenna 28m TX antenna 17m stair case
    Proceedings of the 73rd IEEE Vehicular Technology Conference, VTC Spring 2011, 15-18 May 2011, Budapest, Hungary; 01/2011
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    Ramesh Annavajjala · A. Chockalingam · S.K. Mohammed
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    ABSTRACT: Consider L independent and identically distributed exponential random variables (r.vs) X<sub>1</sub>, X<sub>2</sub>,...,X<sub>L</sub> and positive scalars b<sub>1</sub>, b<sub>2</sub>,...,b<sub>L</sub>. In this letter, we present the probability density function (pdf), cumulative distribution function and the Laplace transform of the pdf of the composite r.v Z = (Σ<sub>(j=1)</sub><sup>L</sup> X<sub>j</sub>)<sup>2</sup>/(Σ<sub>(j=1}</sub><sup>L</sup> b<sub>j</sub> X<sub>j</sub>). We show that the r.v Z appears in various communication systems such as i) maximal ratio combining of signals received over multiple channels with mismatched noise variances, ii) M-ary phase-shift keying with spatial diversity and imperfect channel estimation, and iii) coded multi-carrier code-division multiple access reception affected by an unknown narrow-band interference, and the statistics of the r.v Z derived here enable us to carry out the performance analysis of such systems in closed-form.
    IEEE Transactions on Communications 12/2010; DOI:10.1109/TCOMM.2010.091710.100038 · 1.98 Impact Factor
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    Hobin Kim · Ramesh Annavajjala · Pamela Cosman · Laurence Milstein
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    ABSTRACT: In this paper, we are concerned with the design and analysis of joint source-channel coding schemes for block fading channels with relay-assisted distributed spatial diversity. Assuming a progressive image coder with a constraint on the transmission bandwidth, we formulate a joint source-channel rate allocation scheme that maximizes the expected source throughput. Specifically, using Gaussian as well as BPSK inputs on flat Rayleigh fading channels, we lower bound the average packet error rate by the corresponding mutual information outage probability, and derive the average throughput expression as a function of channel code rates as well as channel SNR for both a frequency-division multiplexing-based baseline system without relaying, and a half-duplex relay system with a decode-and- forward protocol. At high signal-to-noise ratio (SNR), for the systems considered in this paper, we show that our rate optimization problem is a convex function of the channel code rates, and we show that a known recursive algorithm can be used to predict the performance of both systems.
    IEEE Transactions on Communications 07/2010; 58(6-58):1631 - 1642. DOI:10.1109/TCOMM.2010.06.080203 · 1.98 Impact Factor
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    R. Annavajjala · A. Maaref · Jinyun Zhang
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    ABSTRACT: In this paper, we study the impact of uncertain channel state information (CSI) on the performance of demodulate-and-forward relaying protocols with higher order modulation formats such as pulse-amplitude modulation (PAM) and rectangular quadrature-amplitude modulation (QAM). Assuming a single source and a single destination node assisted by N relay nodes, we study the average bit error probability (BEP) performance of M-ary PAM and rectangular QAM constellations with Gray code mapping and imperfect CSI at the relay nodes as well as the destination. The main contributions of this paper are the derivation of closed-form expressions for a) the cumulative distribution functions of the demodulator test statistics, b) the transition probability of error at a given relay, and c) the average BEP for independent and not necessarily identically distributed Rayleigh fading channels with imperfect receiver CSI.
    Communications (ICC), 2010 IEEE International Conference on; 06/2010
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    Ramesh Annavajjala
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    ABSTRACT: This correspondence is concerned with the performance of a regenerative relaying protocol on fading wireless channels with imperfect channel knowledge at the receivers. Assuming a single source and a single destination with multiple relay nodes, using binary modulation at the source, we present optimum receiver at the destination on frequency-flat Rayleigh fading channels by taking into account the effects of imperfect channel knowledge at the receivers. Since exact performance analysis of the optimal receiver is complicated due to the non-linear nature of the log-likelihood ratio contribution from the relay, upon using a standard technique in the literature, we present a simple approximate receiver and derive closed-form expression for the average bit error rate (BER) at the destination with a single relay node. We also present a simple analytical technique that allows us to numerically evaluate the average BER for an arbitrary number of relay nodes. Finally, with perfect channel estimation our proposed receiver subsumes the coherent receivers whereas with a minimum mean-square error channel estimation it reduces to the non-coherent receiver in the work of Chen and Laneman (2006).
    IEEE Transactions on Signal Processing 04/2010; 58(3-58):1928 - 1934. DOI:10.1109/TSP.2009.2038416 · 3.20 Impact Factor
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    Ramesh Annavajjala · Jinyun Zhang
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    ABSTRACT: Knowledge of the level crossing rates (LCR) and average outage durations (AOD) of the received signal-to-interference-plus-noise ratio (SINR) is very useful in designing and analyzing the communication system performance in a cellular environment with co-channel interference (CCI). In this paper, we study the analytical LCR and the AOD of the received SINR on Rayleigh fading channels with CCI. A closed-form expression for the LCR and the AOD is obtained for the general case of multiple co-channel interferers, traveling at different speeds, with unequal powers and with additive white Gaussian noise. We also specialize the derived results to the case of both interference-limited and noise-limited scenarios.
    01/2010; DOI:10.1109/MILCOM.2010.5680111
  • R. Annavajjala · C.R. Murthy
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    ABSTRACT: This paper addresses the design and analysis of practical distributed beamforming techniques for the uplink communication over a wireless sensor network. Since the conventional frequency-division duplexing techniques require a large feedback overhead, we focus on a time-division duplexing approach, and exploit the channel reciprocity to reduce the channel feedback requirement. We consider periodic broadcast of known pilot symbols by the fusion center, and maximum likelihood estimation of the channel phase by the sensor nodes for the subsequent uplink co-phasing transmission. For simplicity, we study binary signaling over frequency-flat fading channels, and quantify the system performance such as the expected gains in the received signal-to-noise ratio (SNR) and the average probability of error at the fusion center, as a function of the number of sensor nodes and the pilot overhead. Our results show that a modest amount of accumulated pilot SNR is sufficient to realize a large fraction of the maximum possible beamforming gain.
    Sensor, Mesh and Ad Hoc Communications and Networks, 2009. SECON '09. 6th Annual IEEE Communications Society Conference on; 07/2009
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    Y. Isukapalli · R. Annavajjala · BD Rao
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    ABSTRACT: In this paper, we analyze the performance of transmit beamforming on multiple-antenna Rayleigh fading channels with imperfect channel feedback. We characterize the feedback imperfections in terms of noisy channel estimation, feedback delay, and finite-rate channel quantization. We develop a general framework, that is valid for an arbitrary two-dimensional linear modulation, to capture the aforementioned imperfections and derive the symbol and bit error probability expressions for both M-PSK and M-ary rectangular QAM constellations with Gray code mapping. We show that the proposed analytical formulation is valid for a frequency-domain duplexing system with/without finite-rate channel quantization and a time-domain duplexing system. We validate the accuracy of the analysis through simulations, and assess the relative effects of channel estimation inaccuracy, feedback delay, and finite-rate quantization on the symbol and bit error performances for various constellations.
    IEEE Transactions on Communications 02/2009; 57(1-57):222 - 231. DOI:10.1109/TCOMM.2009.0901.060354 · 1.98 Impact Factor

Publication Stats

499 Citations
54.18 Total Impact Points

Institutions

  • 2008–2012
    • Mitsubishi Electric Research Laboratories
      Cambridge, Massachusetts, United States
  • 2011
    • Syracuse University
      Syracuse, New York, United States
    • Université du Québec à Montréal
      Montréal, Quebec, Canada
  • 2003–2007
    • University of California, San Diego
      • Department of Electrical and Computer Engineering
      San Diego, California, United States
  • 2003–2004
    • California State University
      • Department of Electrical & Computer Engineering
      Long Beach, California, United States