Browsing by Author "Li, Longguang"

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On the Capacity of Block Fading Optical Wireless Channels
(2019-01-01)
Li, Longguang
;
Moser, Stefan M.
;
Wang, Ligong
;
Wigger, Michele
;
電信工程研究所
This paper investigates the capacity of block fading optical intensity channels with more transmit than receive antennas under different assumptions on the transmitter's channel state information (CSI). Lower and upper bounds on the capacities are derived using the entropy power inequality (EPI) and a dual expression for capacity. Our lower bounds for perfect and partial CSI utilize a transmit-antenna cooperation strategy based on minimum-energy signaling, which we proposed recently. For perfect CSI, this lower bound matches the upper bound asymptotically in the high signal-to-noise ratio (SNR) regime. For imperfect CSI, our lower bound is close to its perfect-CSI counterpart.
On the Capacity of MIMO Optical Wireless Channels
(2020-09-01)
Li, Longguang
;
Moser, Stefan M.
;
Wang, Ligong
;
Wigger, Michele
;
電信工程研究所
This paper studies the capacity of a general multiple-input multiple-output (MIMO) free-space optical intensity channel under a per-input-antenna peak-power constraint and a total average-power constraint over all input antennas. The focus is on the scenario with more transmit than receive antennas. In this scenario, different input vectors can yield identical distributions at the output, when they result in the same image vector under multiplication by the channel matrix. We first determine the most energy-efficient input vectors that attain each of these image vectors. Based on this, we derive an equivalent capacity expression in terms of the image vector, and establish new lower and upper bounds on the capacity of this channel. The bounds match when the signal-to-noise ratio (SNR) tends to infinity, establishing the high-SNR asymptotic capacity. We also characterize the low-SNR slope of the capacity of this channel.
On the Capacity of MIMO Optical Wireless Channels
(2018-01-01)
Li, Longguang
;
Moser, Stefan M.
;
Wang, Ligong
;
Wigger, Michele
;
電信工程研究所
This paper investigates the capacity of the multiple-input multiple-output free-space optical intensity channel under a per-input-antenna peak-power constraint and a total average-power constraint over all input antennas. Our work considers the setup with more transmit than receive antennas, and characterizes capacity as an alternative optimization problem over the distribution of the input vector times the channel matrix. This alternative capacity expression is then used to obtain upper and lower bounds on the capacity, which match asymptotically in the high signal-to-noise ratio regime.
The MISO Free-Space Optical Channel at Low and Moderate SNR
(2018-01-01)
Li, Longguang
;
Moser, Stefan M.
;
Wang, Ligong
;
Wigger, Michele
;
電信工程研究所
The capacity of the multiple-input single-output (MISO) free-space optical channel with a per-antenna peak-power constraint and a sum (over all antennas) average-power constraint is studied. The asymptotic low-signal-to-noise-ratio (low-SNR) capacity is determined exactly and close upper and lower bounds are presented in the low-and moderate-SNR regimes. The asymptotic low-SNR limit is achieved by having each transmit antenna signal either with zero or with the maximally allowed peak power, and the latter only if all stronger antennas also send at maximum peak power. In particular, for almost all channel gains, the input to achieve the asymptotic low-SNR capacity is such that its projection on the channel-gain vector has only two or three positive probability point masses, one of them being at zero. The lower bounds at finite SNR are numerical and are obtained using input distributions whose projection on the channel-gain vector has either two, three, or four positive probability masses. Finally, the paper presents two analytic upper bounds on the capacity of the MISO channel: the first one closely follows the proposed numerical lower bounds in the low-SNR regime, and the second one can improve on previous bounds in the moderate-SNR regime.