With the growing demand for bandwidth and transmission speed, mobile communication network designs must stay adaptable, efficient and cost-effective. A key integration has been Radio-over-Fiber (RoF) transmission systems that provide a cheaper option and low loss for high frequency signal transfer. For the optical transmitter, delta-sigma modulation (DSM) can be a beneficial addition. The partnership simplifies the Digital-Radio-over-Fiber setup by removing the need for additional converters and prompts adjustments based on system need. Main factors in delta-sigma modulators are the amount of quantization bits and the order of the modulator. Changing quantization bits to a single bit allows the system to use less processing bandwidth and less error experienced from optical transmission. High order structures provide more noise shaping to shift noise away from the band of interest. Still, such setups are prone to linearity problems due to clock jitter from multiple feedback loops.
Different adaptations of delta-sigma modulation have been designed to combat the problems, but a key standout is the implementation of an envelope delta-sigma modulation (EDSM). Envelope delta-sigma modulation’s separate processing of envelope and phase delivers time alignment and noise shaping counter the negative implications from high order DSMs. Combining envelope delta-sigma modulation with RoF transmission is an attractive option, but research has yet to delve into carrier aggregation with these setups.
This thesis explores concurrent dual band 64-QAM 20 MHz LTE Radio-over-Fiber using 1-bit envelope delta-sigma modulation. It expands transmitter functionality by concurrent signal integration. Inside the EDSM is a 4th order bandpass delta-sigma modulator custom tailored one of two carrier frequencies. The two frequencies come from two different LTE bands to show interband compatibility. The carrier frequencies are 2.112 GHz from LTE band 1 and 2.64 GHz from LTE band 7.
Simulation and experimental results confirm the functionality of the proposed envelope delta-sigma modulation RoF system in single and dual band for LTE standards (error vector magnitude < 8%). Experimental results confirm that EDSM is more resilient to RoF transmission than BP-DSM. However, the EVM values for BP-DSM are better for carrier aggregated transmission
