Orbital angular momentum (OAM) multiplexing can improve the transmission efficiency and provide higher bandwidth for underwater wireless optical communication (UWOC). However, the turbulence effect in ocean would indu...
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ISBN:
(纸本)9781665443852
Orbital angular momentum (OAM) multiplexing can improve the transmission efficiency and provide higher bandwidth for underwater wireless optical communication (UWOC). However, the turbulence effect in ocean would induce the crosstalk between OAM modes, thereby leading to the reliability performance degradations. In this paper, we first utilize the mode modulation in the underwater OAM multiplexing system to deliver extra information bits. Then we add a zero-forcing (ZF) based precoder at the transmitter to mitigate the crosstalk effects to enhance the reliability performances. At the receiver, we propose a two-step maximum likelihood (TSML) detector which has lower complexity than that of the ML detection to recover the transmitted symbols. Moreover, we derive the bit error rate (BER) expressions for the proposed systems operating under perfect or imperfect channel state information (CSI) conditions, and the simulation results validate the theoretical analysis. Last but not the least, the simulated performances of the proposed system under different underwater channel parameters, e.g. the dissipation rate of temperature, the relative strength of temperature and salinity fluctuations and turbulence strengths are investigated and analyzed.
The optimization of zero-forcing precoders is studied for the structural similarity (SSIM) index in this paper. When the input signal is an image for the multi-user multi-input multi-output (MIMO) downlink communicati...
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ISBN:
(纸本)9781728101057
The optimization of zero-forcing precoders is studied for the structural similarity (SSIM) index in this paper. When the input signal is an image for the multi-user multi-input multi-output (MIMO) downlink communication channels. the traditional precoders design with maximizing signal to noise ratio(SNR) or mean squared error(MSE) may not retain the structural information of transmitted signal. In this paper, we consider the problem of linear precoding design with SSIM index under the weak zero-forcing condition. A general solution for zero-forcing precoder is provided to guarantee the quality of the received image, under total power constraint or per-antenna power constraint. The precoder design with SSIM is a non-convex problem. We use the polynomial fitting method to convert it into convex problem, and then use the convex optimization toolbox to solve it. Experiment results have shown the effectiveness and advantages of the proposed precoder.
In this paper, a multiuser space-time line code (STLC) system is proposed. In the proposed multiuser STLC system, a zero-forcing (ZF)-based precoder decomposes multiuser multiple-input multiple-output (MIMO) channels ...
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In this paper, a multiuser space-time line code (STLC) system is proposed. In the proposed multiuser STLC system, a zero-forcing (ZF)-based precoder decomposes multiuser multiple-input multiple-output (MIMO) channels into multiple single-user MIMO channels, and the STLC is performed with the effective single user MIMO channel independently for each user. Here, to maximize the sum rate, an optimal power allocation method is designed based on a water-filling strategy. Also, a simple suboptimal method called fairness-aware per-user (FAPU) power allocation is devised. It is analytically and numerically verified that each user of the proposed ZF-based STLC system asymptotically achieves the maximum of single-user achievable rate as the number of transmit antennas increases. The numerical results of rigorous simulation justify that the proposed ZF-based STLC with FAPU power allocation provides near optimal performance and outperforms the existing ZF-based maximum Eigen beamforming scheme and conventional multiuser STLC schemes. Furthermore, two simple search algorithms to find the optimal number of users that maximizes sum rate are devised. Numerical results verify that the proposed algorithms can effectively find the optimal number of users by reducing the search interval.
Full frequency reuse based dual satellite system (DSS) is investigated in this work. In the case of DSS, user terminals receive inter spot beam and intra spot beam interfering signals due to the simultaneous transmiss...
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Full frequency reuse based dual satellite system (DSS) is investigated in this work. In the case of DSS, user terminals receive inter spot beam and intra spot beam interfering signals due to the simultaneous transmission of data from both satellites. Cooperative precoding algorithm is proposed to mitigate these effects. The achievable data rates with zero-forcing (ZF) and regularized ZF precoding algorithms are characterized. If the user terminals served by both satellites are colocated, then the proposed cooperative precoding algorithm fails because of correlated channels. To this end, relay-aided DSS (RA-DSS) is proposed. The achievable data rates of both full-duplex and half-duplex RA-DSSs are characterized. Through simulations, it is shown that the proposed full-duplex RA-DSS achieves better data rate than the DSS, single satellite system, and orthogonal transmission even if the users are closely placed.
In this paper, we analyze and optimize the energy efficiency (EE) of multi-user (MU) multiple-input and multiple-output (MIMO) in downlink multi-cell networks. We first analyze the spectral efficiency (SE) of MU-MIMO ...
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In this paper, we analyze and optimize the energy efficiency (EE) of multi-user (MU) multiple-input and multiple-output (MIMO) in downlink multi-cell networks. We first analyze the spectral efficiency (SE) of MU-MIMO systems with a huge number of base station (BS) antennas by using maximal ratio transmission (MRT) and zero-forcing (ZF) precoders in downlink cellular networks. In the analysis, we assume that the number of the BS antennas is huge but limited, which is different from the conventional analysis. Then, we use the analytical SE result and the EE definition to obtain the system EE expression and further analyze the effect of the number of BS antennas and the number of served users on system EE. Since the system EE on the numbers of BS antennas and the number of served users is approximately concave, the corresponding iterative optimization algorithms are proposed to achieve the maximum system EE. The computer simulation results show that the analytical results are accurate and each served user needs about 2 active BS antennas to obtain the maximum system EE when the channel state information is available at the transmitter. (C) 2018 Elsevier Inc. All rights reserved.
We study the effects of residual carrier frequency offset (CFO) on the performance of the distributed zero-forcing (ZF) beamformer. Coordinated transmissions, where multiple cells cooperate to simultaneously transmit ...
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We study the effects of residual carrier frequency offset (CFO) on the performance of the distributed zero-forcing (ZF) beamformer. Coordinated transmissions, where multiple cells cooperate to simultaneously transmit toward one or multiple receivers, have gained much attention as a means to provide the spectral efficiency and data rate targeted by emerging standards. Such schemes exploit multiple transmitters to create a virtual array of antennas to mitigate the co-channel interference and provide the gains of multi-antenna systems. Here, we focus on a distributed scenario where the transmit nodes share the same data but have only the local knowledge of the channels. Considering the distributed nature of such schemes, time/frequency synchronization among the cooperating transmitters is required to guarantee good performance. However, due to the Doppler effect and the non-idealities inherent to the local oscillator embedded in each wireless transceiver, the carrier frequency at each transmitter deviates from the desired one. Even when the transmitters perform frequency synchronization before transmission, a residual CFO is to be expected that degrades the performance of the system due to the in-phase misalignment of the incoming streams. This paper presents the losses of the signal-to-noise ratio gain analytically and the diversity order semi-numerically of the distributed ZF beamformer for the ideal case and in the presence of a residual CFO. We illustrate our results and their accuracy through simulations.
This paper proposes a precoding scheme for downlink multiuser MIMO-OFDM systems. The proposed precoding employs the minimum bit error rate (BER) criterion and estimates precoding matrices to minimize total BER of mobi...
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ISBN:
(纸本)9781424480166
This paper proposes a precoding scheme for downlink multiuser MIMO-OFDM systems. The proposed precoding employs the minimum bit error rate (BER) criterion and estimates precoding matrices to minimize total BER of mobile stations by the steepest descent algorithm. As the cost function of the proposed scheme, an upper bound of the total BER is derived from the pairwise error probability (PEP) and is averaged with respect to channel state information (CSI) errors. Thus, the proposed scheme can be robust to imperfect CSI. Computer simulations under a frequency-selective fading condition demonstrate that the proposed precoder is more robust to the CSI errors than the zero-forcing (ZF) precoder, and that it is superior in BER to the conventional scheme.
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