OFDM allocation optimization for crosstalk mitigation in multiple free-space optical interconnection links

The growing demand for high interconnection speed in next-generation computers is driving the technology shift for communication from the electronic to the optic domain. One of the favored interconnection technologies for this task is the free-space optical interconnect (FSOI). FSOI technology uses laser links between computer components and provides a lower bound on propagation delay due to the low index of refraction of air, when compared with the indexes common in waveguide technologies. FSOIs based on dc-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) may provide excellent data throughput in intensity modulation/direct detection systems. However, the main drawback limiting the implementation of FSOIs is the inevitable tradeoff between interconnection density and the crosstalk level, resulting from the diffraction effect and from optical misalignment. The purpose of this paper is to promote improved interconnection density of such FSOIs by use of inherent DCO-OFDM resource allocation capabilities. The crosstalk-resulted interference was formulated as joint multilink bit-and-power allocation optimization. The theoretical analysis reveals general guidelines for dense FSOI. Further, a reduced-complexity numerical suboptimal algorithm for joint multilink bit-and-power allocation was proposed. The simulation results show that the proposed suboptimal algorithm outcome is close to the theoretical optimal performance.