Hybrid pulse position modulation/ultrashort light pulse code division multiple access for data networking

Future data networks are required to support numerous high-capacity connections while providing simplified management and connectivity. To meet these requirements, we propose to utilize broadband ultrashort light pulses (ULP) in conjunction with pulse position modulation (PPM) as an efficient modulation format and code division multiple access (CDMA) for interference suppression. This networking format is operated asynchronously for simplified control, and requires minimal management for ensuring that the number of active users is below the limit at which multi-user interference generates excessive errors. The pulse positions can be detected at the receiver with high temporal resolution by utilizing a time-to-space conversion operating in real-time. The performance of the PPM/ULP-CDMA is found to depend on the following parameters: the ULP duration, the bandwidth of each spectral chip of the CDMA filter, and the ULP repetition time. We find that employing PPM improves the performance of the system relative to On-Off Keying (OOK). The performance can be further improved by increasing the number of PPM symbols, reducing the spectral chip bandwidth, and reducing the ratio of the pulse duration to repetition time. The performance analysis shows that the proposed system operates at a high bandwidth efficiency.