Many wireless communication problems is based on a convex relaxation of the maximum likelihood problem which further can be cast as binary quadratic programs (BQPs). The two standard relaxation methods that are widely...
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Many wireless communication problems is based on a convex relaxation of the maximum likelihood problem which further can be cast as binary quadratic programs (BQPs). The two standard relaxation methods that are widely used for solving general BQPs such as spectral methods and semidefinite programming problem (SDP), each have their own advantages and disadvantages. It is widely accepted that small and medium sized SDP problems can be solved efficiently by interior point methods. Albeit, semidefinite relaxation has a tighter bound for large scale problems, but its computational complexity is high. However, Row-by-Row method (RBR) for solving SDPs could be opted for an alternative for large-scale MIMO detection because of low complexity. The present work is a spectral SDP-cut formulation to which the RBR is applied for large-scale MIMO detection. A modified RBR algorithm with tighter bound is presented to specify the efficiency in detecting massive MIMO.
One of the main challenges in high-speed mobile communications is the presence of large Doppler spreads. Thus, accurate estimation of maximum Doppler spread (MDS) plays an important role in improving the performance o...
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One of the main challenges in high-speed mobile communications is the presence of large Doppler spreads. Thus, accurate estimation of maximum Doppler spread (MDS) plays an important role in improving the performance of the communication link. In this paper, we derive the data-aided (DA) and non-data-aided (NDA) Cramer-Rao lower bounds (CRLBs) and maximum likelihood estimators (MLEs) for the MDS in multiple-input multiple-output (MIMO) frequency-selective fading channel. Moreover, a low-complexity NDA-moment-based estimator (MBE) is proposed. The proposed NDA-MBE relies on the second-and fourth-order moments of the received signal, which are employed to estimate the normalized squared autocorrelation function of the fading channel. Then, the problem of MDS estimation is formulated as a non-linear regression problem, and the least-squares curve-fitting optimization technique is applied to determine the estimate of the MDS. This is the first time in the literature, when DA- and NDA-MDS estimation is investigated for MIMO frequency-selective fading channel. Simulation results show that there is no significant performance gap between the derived NDA-MLE and NDA-CRLB, even when the observation window is relatively small. Furthermore, the significant reduced-complexity in the NDA-MBE leads to low root-mean-square error over a wide range of MDSs, when the observation window is selected large enough.
Visible light communication (VLC) is regarded as one of the promising candidates to complement the conventional radio frequency communication as it can potentially perform communication and illumination simultaneously...
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Visible light communication (VLC) is regarded as one of the promising candidates to complement the conventional radio frequency communication as it can potentially perform communication and illumination simultaneously. Recently, VLC is combined with the generalized spatial modulation (GenSM) technology to improve spectral and energy efficiencies. In order to provide high-speed communication and flexible dimming control simultaneously, in this paper, a spectral-efficient GenSM-based hybrid dimming scheme with layered asymmetrically clipped optical OFDM is proposed for VLC, which combines the spatial-domain and time-domain dimming strategies. The channel capacities of the proposed scheme are analyzed and the closed-form expressions of the channel capacity are derived in both the rich scattering scenario and highly correlated scenario. According to the required illumination level, the spatial-domain and time-domain strategies are realized based on the maximization of the channel capacity. Simulation results substantiate the superior performance of the proposed dimming scheme over the state-of-art dimming schemes.
We propose the optimum design of high spatial density few-mode multicore fiber (MCF) for repeated space-division multiplexed (SDM) transmission. Numerical analyses reveal that a hexagonally arranged six-mode seven-cor...
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We propose the optimum design of high spatial density few-mode multicore fiber (MCF) for repeated space-division multiplexed (SDM) transmission. Numerical analyses reveal that a hexagonally arranged six-mode seven-core structure is potentially better than the other possibility, the six-mode multicore structure, in terms of realizing high spatial density and low mode-dependent loss (MDL) characteristics at the splice point;its benefits will enable us to construct long-haul dense SDM transmission links. We fabricate a 171 mu m cladding six-mode seven-core fiber and successfully demonstrate low loss, differential mode delay (DMD), crosstalk, and splice-induced MDL characteristics while maintaining the relative core multiplicity factor of more than 50. Finally, we demonstrate repeated optical 12 x 12 MIMO transmission of more than 100 km using our six-mode MCF and erbium doped fiber amplifier (EDFA).
Space time block code (STBC) and vertical Bell layered space-time (VBLAST) signals are widely applied in multiple-input multiple-output (MIMO) systems, and one essential step in the signal interception process is to r...
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Space time block code (STBC) and vertical Bell layered space-time (VBLAST) signals are widely applied in multiple-input multiple-output (MIMO) systems, and one essential step in the signal interception process is to recognize STBC/VBLAST. As the STBC signal is correlated in time, it has a specific cyclic frequency in higher-order cyclic accumulation, while the VBLAST signal emitted from different antenna is uncorrelated. According to this property, this paper proposes a blind recognition approach for STBC/VBLAST signals based on fourth-order cyclic accumulation (FCC). The recognition process is divided into two steps. In the first step, we first establish the correlation choosing criteria that makes sure all correlations of STBC can generate a statistically cyclic sequence. The cyclic statistic then is estimated by combining the FCC with channel information that provides the peaks phase of the statistically cyclic sequence. The second step compares the estimated cyclic statistic with a detection threshold, which is obtained by given a probability of false alarms. The proposed approach avoids the need for any prior knowledge of the transmitted signal, and can work well in the lowly SNR by employing the advantages of FCC. (C) 2018 Elsevier Inc. All rights reserved.
A geometry-based stochastic scattering model （GBSSM） based on geometrical multiple rings and ellipses is proposed for wideband multiple-input multiple-output （MIMO） mobile-to-mobile （M2M） fading channels. The pr...
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A geometry-based stochastic scattering model （GBSSM） based on geometrical multiple rings and ellipses is proposed for wideband multiple-input multiple-output （MIMO） mobile-to-mobile （M2M） fading channels. The proposed GBSSM is deployed with cross-polarized antennas and can be applied for the line-of-sight （LOS） and non- LOS （NLOS） scenarios by considering the single-bounced （SB） and double-bounced （DB） components. The channel realization is much more straightforward and concise to study the channel characteristics compared with the too complicated analytical solutions available so far. Based on the proposed GBSSM and realized channel, the channel characteristics and parameters at 2 GHz and 5 GHz with 100 MHz bandwidth are further investigated. The results can be used in the link and system level simulations in M2M radio systems.
This paper investigates the keyhole or pinhole effect on the pairwise error probability (PEP) performance of the multiple-input multiple-output (MIMO) space-time block-code (STBC) based selective decode and forward (S...
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This paper investigates the keyhole or pinhole effect on the pairwise error probability (PEP) performance of the multiple-input multiple-output (MIMO) space-time block-code (STBC) based selective decode and forward (S-DF) protocol. The closed form PEP expressions are derived for several configurations in terms of number of hops, phases, and relays over Nakagami-m fading channel, with perfect and imperfect channel state information (CSI), and with and without the keyhole condition. Further, a framework is developed for deriving the diversity order (DO) for each configuration. It demonstrates that full DO for cooperation protocol can be achieved when there is a knowledge of perfect CSI. A convex optimization framework is formulated for obtaining the optimal source-relay power allocation factors which significantly improve the end-to-end reliability of the system under power constraint scenarios. Monte Carlo simulations are performed for both equal and optimal power allocation factors and results show the substantial improvement in PEP performance with an increase in the value of the shape parameter and relay to destination (RD) link channel variance. Results show an improved PEP performance by increasing the RD link channel variance in comparison to increasing the source to relay (SR) link channel variance. Also PEP performance degrades for keyhole Nakagami-m fading channel as compared to Nakagami-m fading channel. Simulation results are in close agreement with the analytical results at high signal to noise ratio (SNR) regimes. (C) 2018 Elsevier B.V. All rights reserved.
In this paper, the power allocation problem in a relay-assisted cognitive radio network (CRN) is considered where the secondary users exchange information in an interweave mode on the basis of physical layer network c...
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In this paper, the power allocation problem in a relay-assisted cognitive radio network (CRN) is considered where the secondary users exchange information in an interweave mode on the basis of physical layer network coding. In order to enhance the capacity of CRN, using multiple-input multiple-output and orthogonal frequency division multiplexing has become very popular in the literature. This paper goes one step further to improve the throughput of secondary users using physical layer network coding by drawing off the transmission time. The main goal is to maximize the capacity of CRN, while keeping the total interference imposed on the primary users under a certain threshold. An optimal solution to this power allocation problem with limited relay power constraint, due to the limited budget, is derived;however, because of the high complexity of this method, an efficient suboptimal solution is also proposed.
In this paper, we have experimentally demonstrated the feasibility of space-division-multiplexed 3 x 3 multiple-input multiple-output (MIMO) transmission over a single OM3 multimode fiber (MMF) using commercial IEEE 8...
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In this paper, we have experimentally demonstrated the feasibility of space-division-multiplexed 3 x 3 multiple-input multiple-output (MIMO) transmission over a single OM3 multimode fiber (MMF) using commercial IEEE 802.11 n/ac access points. Throughput performance for different fiber length links under a range of fiber bending conditions was evaluated. To study the throughput improvement by MIMO technology, throughput performance of single-input single-output (SISO), 2 x 2 MIMO and 3x3MIMO over separate SMF links was also measured for comparison. It is shown that, spatially-multiplexed MMF channel with 3x3MIMO configuration could provide a significant throughput increase in comparison with SISO and 2x2MIMO SMFs configurations, and present a comparable performance with 3x3MIMO SMFs configuration. Meanwhile, the analyses of the impact of fiber bending indicate that, even under a tight fiber bending radius as low as 2 mm, the system performance could still keep at an acceptable level. With all fiber bending radii tested, within each 5-min measurement time, the fiber channel is found to be good enough to provide throughput greater than twice the average SISO value for more than 87.66% and 72.72% of the time, at the 2.4 and 5 GHz bands, respectively. These results together point out a very simple and cost-saving solution for future in-building DASs to distribute wireless MIMO signals using commercially-availableMMFinfrastructure by space division multiplexing technique, even though it may encounter tight bending conditions.
The generalized spatial modulation (GSM) is a new transmission technique that can realize high-performance multiple-input multiple-output (MIMO) communication systems with a low RF complexity. This paper presents an e...
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The generalized spatial modulation (GSM) is a new transmission technique that can realize high-performance multiple-input multiple-output (MIMO) communication systems with a low RF complexity. This paper presents an efficient sphere decoding method used to perform the symbol detection for the generalized spatial modulation (GSM) multiple-input multiple-output (MIMO) systems. In the proposed method, the cost metric is modified so that it does not include the cancellation of the nonexistent interference. The modified cost metric can be computed by formulating a detection tree that has a regular structure representing the transmit antenna combinations as well as the symbol vectors, both of which are detected efficiently by finding the shortest path on the basis of an efficient tree search algorithm. As the tree search algorithm is performed for the regular detection tree to compute the modified but mathematically-equivalent cost metric, the efficiency of the sphere decoding is improved while the biterror rate performance is not degraded. The simulation results show that the proposed method reduces the complexity significantly when compared with the previous method: for the 6 +/- 6 64QAM GSM-MIMO system with two active antennas, the average reduction rate of the complexity is as high as 45.8% in the count of the numerical operations.
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