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IEEE Transactions on Wireless Communications. 01/2011; 10:2681-2691.
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IEEE Transactions on Wireless Communications. 01/2011; 10:456-465.
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2011 IEEE Wireless Communications and Networking Conference, WCNC 2011, Proceedings, Cancun, Mexico, 28-31 March, 2011; 01/2011
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Proceedings of IEEE International Conference on Communications, ICC 2011, Kyoto, Japan, 5-9 June, 2011; 01/2011
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European Transactions on Telecommunications. 01/2011; 22:125-136.
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ABSTRACT: Super-imposed training can be used as an alternative solution to estimating the channel state information (CSI). Since pilots are sent together with the data symbols, superimposed training improves the bandwidth efficiency. In this paper, we study the effects of the channel estimation errors on binary phase shift keying (BPSK) systems using superimposed pilots. Specifically, we derive an approximate bit error rate (BER) expression in low signal-to-noise ratio (SNR) region while in high SNR region, we derive the lower bound of the BER. Simulation results are then provided to corroborate the proposed studies.
Wireless Communications, Networking and Information Security (WCNIS), 2010 IEEE International Conference on; 07/2010
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ABSTRACT: In this paper, we consider an interesting and practical scenario for spectrum sensing in cognitive radio network, where both the signal power of the primary user and the noise variance are treated as unknowns before the detection. Knowing accurate noise variance and signal power is crucial in most sensing algorithms, e.g., energy detection. By exploiting the received signal structure, we propose blind spectrum sensing methods in the sense that both the signal power of the primary user and the noise variance are estimated, which is a non-trivial task before knowing the status of the primary user. Three different algorithms, direct estimator, approximate maximum likelihood (ML) estimator and pseudo linear minimum mean square error (MMSE) estimator, are proposed based on the moments of received signals. Simulation results confirm that the proposed algorithms can estimate the noise variance and the primary user's signal power with high accuracy.
Wireless Communications and Networking Conference (WCNC), 2010 IEEE; 05/2010
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Proceedings of the Global Communications Conference, 2010. GLOBECOM 2010, 6-10 December 2010, Miami, Florida, USA; 01/2010
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2010 IEEE Wireless Communications and Networking Conference, WCNC 2010, Proceedings, Sydney, Australia, 18-21 April 2010; 01/2010
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Proceedings of the Global Communications Conference, 2008. GLOBECOM 2008, New Orleans, LA, USA, 30 November - 4 December 2008; 01/2008
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IEEE Transactions on Communications. 01/2008; 56:1425-1429.
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Proceedings of the Global Communications Conference, 2008. GLOBECOM 2008, New Orleans, LA, USA, 30 November - 4 December 2008; 01/2008
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Proceedings of IEEE International Conference on Communications, ICC 2007, Glasgow, Scotland, 24-28 June 2007; 01/2007
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IEEE Communications Letters. 01/2005; 9:423-425.
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ABSTRACT: In this paper, we answer the question that “Can conventional
differential unitary space time modulation (DUSTM)
be applied when there is an unknown carrier frequency offset
(CFO)?” and present a maximum likelihood (ML) detection rule
for this scenario. We analyze the asymptotical performance of our
ML detection and provide the code design criterion by using the
modified diversity product. The analysis also brings the insight
that our proposed decision rule is a new differential modulation
scheme in both temporal and spatial domains. Various simulations
are conducted, and the proposed algorithm is shown to
be more robust to the CFO drifting than the existing double
temporal differential modulation.
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ABSTRACT: We show a statistical pruning approach for maximum
likelihood (ML) detection of multiple-input multiple-output
(MIMO) systems. We present a general pruning strategy for
sphere decoder (SD), which can also be applied to any tree search
algorithms. Our pruning rules are effective especially for the case
when SD has high complexity. Three specific pruning rules are
given and discussed. From analyzing the union bound on the
symbol error probability, we show that the diversity order of the
deterministic pruning is only one by fixing the pruning probability.
By choosing different pruning probability distribution
functions, the statistical pruning can achieve arbitrary diversity
orders and SNR gains. Our statistical pruning strategy thus
achieves a flexible trade-off between complexity and performance.
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ABSTRACT: Frequency synchronization is one of the most important
components in orthogonal frequency-division multiplexing
(OFDM) systems. Recently, the discrete cosine transform (DCT)
based OFDM system has received wide attentions due to several
advantages. Hence, the study of frequency synchronization issue
for this newly raised system is well on its time. To provide
a thorough study, we consider the non-circular transmissions,
and the results can be easily generated to circular transmissions
if the elliptic variance is set to zero. We present three joint
maximum likelihood (ML) carrier frequency offset (CFO) and
phase offset (PO) estimators. From both the theoretical analysis
and the numerical comparisons, we found new advantages of
the DCT-OFDM over the traditional discrete Fourier transform
(DFT) based OFDM. These advantages, as well as those already
studied in the early works on DCT-OFDM, support the belief that
the DCT-OFDM is a new promising multi-carrier modulation
(MCM) scheme.
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ABSTRACT: This work considers two-way relay channels (TWRC), where two terminals transmit simultaneously to each other with the help of a relay node. For single antenna systems, we propose several new transmission schemes for both amplify-and-forward (AF) protocol and decode-and-forward (DF) protocol where the channel state information is not required. These new schemes are the counterpart of the traditional noncoherent detection or differential detection in point-to-point communications. Differential modulation design for TWRC is challenging because the received signal is a mixture of the signals from both source terminals. We derive maximum likelihood (ML) detectors for both AF and DF protocols, where the latter can be considered as performing differential network coding at the physical layer. As the exact ML detector is prohibitively complex, we propose several suboptimal alternatives including decision feedback detectors and prediction-based detectors. All these strategies work well as evidenced by the simulation results. The proposed protocols are especially useful when the required average data rate is high. In addition, we extend the protocols to the multiple-antenna case and provide the design criterion of the differential unitary space time modulation (DUSTM) for TWRC.
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ABSTRACT: In this paper, we consider efficient blind decoder design for orthogonal space-time block codes (OSTBCs). A general decision rule for blind OSTBC decoding is derived assuming a quasi-static flat multiple-input multiple-output (MIMO) Rayleigh fading channel. We use the linear dispersion representation of OSTBCs to derive a blind decoder that results in a quadratic minimization problem, which can be solved efficiently by semidefinite relaxation, sphere decoding or successive interference cancellation. To resolve phase ambiguity problems inherent in blind detectors, rather than using pilot symbols that results in a bandwidth loss, we propose novel totally blind decoders using dual constellations or a superimposed training scheme. To alleviate the computational burden, a minimum mean-squareerror (MMSE) channel estimator is also proposed to track the time-varying channel without using the blind decoder.
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ABSTRACT: In this paper, we consider the signal detection for space-time block coding over time-selective fading channels. We derive a general maximum likelihood (ML) decision rule for space-time block coding (STBC). The resulting detector is valid for any number of receive antennas and for all STBC systems that have the linear dispersion property. The detector results in a quadratic minimization problem, which can be solved efficiently by sphere decoding or nulling-and-cancelling detection. For orthogonal STBC systems, we also propose a suboptimal detector using the principle of parallel interference cancellation (PIC) that is valid for systems with an arbitrary number of receive antennas.
