correlation based preamble detection

i'm working on wireless sensor networks. in the packet transmitted i understand what preamble is. Its just to indicate the receiver that a packet is der to be received. can someone please tell me what is PLH. is plh used to indicate source and destination???? am i right??
My main doubt is what is correlation (in simple words not with mathematical function) and what is correlation based preamble detection??
Why is it used??? (i mean how is it advantageous than other methods)
the paper i read was put that preamble detection results in high power consumption at the receiver side. Pls tell me what causes power consumption at the receiver side??? does correlation cause it and if yes how does it cause????
i want to work on reducing this power consumption. my prof told me to work on the correlator in such a way that i simplify the process where detection consumes less power... he also mentioned something where since the preamble is spread (ie the signal is below noise level), energy simplification cannot work... wat does he mean by energy and why wont it work.. so like what can be done at the correlator which reduces power consumption or is there any other type of detection of preamble other than correlation method?? i know its lot of questions but can someone pls help

The receiver can waste a lot of power waiting for an addressable message. It can also get a lot of data errors if it detects an invalid preamble as true. Preambles for receiver designs tend to have a unique pattern for the preamble that does not occur often in data and gives anadvantage that is tolerant to noise with some bits detected in error. When this is implemented well, Preamble Sync error rates prove to be much better than bit error rates. Thus more tolerant of initial frequency error and require less power before the full receiver channel processing powers are enabled.

This method of Preamble Synchronization is best done using various Auto-Correlation methods.

This may include repetition of a bit sequence which is based on the Barker Code from 1953.

Other methods benefit from using a Matched Filter channel such as "Raised Cosine or Square Root Raised Cosine" to raise the SNR.

Another may include synchronous detection with multiple offset channels with incremental phase/frequency for accumlating and integrating phase error and multiple detection for discriminating bit sync and integrating the error using fewer bits of resolution in the DSP to save power.


By looking at the Barker Code, the number of bits that match the expected pattern peaks when all bits match the expected pattern and falls quickly by each bit shift away from "Sync" due to the Autocorrelation function. Using repeating Barker Code patterns also improves error detection rate which thus saves powering the receiver to process noise.

https://en.m.wikipedia.org/wiki/Barker_code#/image/File:Barker7corr.svg

A review of existing and published methods for Auto-Correlation Preamble might expand on my suggestions.

One must be mindful also of false preambles in other data messages for other users , as well as using a pattern length that is not sensitive to timing error of the Receiver initial frequency or phase.