In this paper, we investigate the capacity of a multiple-input multiple-output (MIMO) optical intensity channel (OIC) under per-antenna peak- and average-intensity constraints. We first consider the case where the average intensities of input are required to be equal to preassigned constants due to the requirement of illumination quality and color temperature. When the channel graph of the MIMO OIC is strongly connected, we prove that the strongest eigen-subchannel must have positive channel gains, which simplifies the capacity analysis. Then we derive various capacity bounds by utilizing linear precoding, generalized entropy power inequality, and QR decomposition, etc. These bounds are numerically verified to approach the capacity in the low or high signal-to-noise ratio regime. Specifically, when the channel rank is one less than the number of transmit antennas, we derive an equivalent capacity expression from the perspective of convex geometry, and new lower bounds are derived based on this equivalent expression. Finally, the developed results are extended to the more general case where the average intensities of input are required to be no larger than preassigned constants.

翻译：本文研究了在每天线峰值与平均强度约束下多输入多输出（MIMO）光强度信道（OIC）的容量问题。首先考虑因照明质量与色温需求而要求输入平均强度等于预设常数的情形。当MIMO OIC的信道图强连通时，我们证明最强特征子信道必须具有正信道增益，这简化了容量分析。随后利用线性预编码、广义熵功率不等式和QR分解等方法推导了多种容量界。数值验证表明，这些界在低信噪比或高信噪比区域能逼近信道容量。特别地，当信道秩比发射天线数少一时，我们从凸几何视角导出了等效容量表达式，并基于该表达式推导了新的下界。最后，将所得结果推广至输入平均强度不大于预设常数的更一般情形。