In this work, we evaluate preamble patterns of IEEE P802.15.4k Low Energy Critical Infrastructure Monitoring Networks (LECIM) DSSS PHY. Due to energy constraints of the P802.15.4k systems, preambles should have robust performance to realize high throughput at low Eb/No situations. Our results reveal that the detection performances of the proposed 2-octet and 4-octet preambles are not adequate. For the case of 4-octet preamble, the main drawback is poor pattern design. To improve the performance of the 4-octet preamble, we propose a novel pattern. The new 4-octet preamble pattern achieves the required detection rate of 10-3 at the target Eb/No of 4 dB. For the case of the 2-octet preamble, its length is the limiting factor. We focus on the receiver side techniques. We propose using aperture and flywheel techniques to improve detection. Using these techniques, target detection rate is achieved and higher throughputs at low Eb/No values are enabled.