You can find several recent and less recent surveys on wireless sensor networks by running a google search with "wireless sensor networks survey" as the search phrase. That should be sufficient to get you started.
Give Search on Wireless Sensor Networks and specially read papers published in journals in this topic....moreover some online free e books also available on this subject. That will hep anyone to start work in this field.
If you are just starting out, then you probably should read "Wireless Sensor Networks: A Survey" (as VR. indicated, indeed by F.Akyildiz). It's a decade old, though, so take it more as "background" and an enumeration of challenges, than as survey of state-of-the-art of today. I attach a link to that paper.
Jonathan Hui's PhD thesis might actually also make a good entry point, being a bit more recent, and (by virtue of having the page-count of a thesis) covering a good bit of ground. I also attach a link to where you can pick up his thesis.
Second, WSN is a rather broad topic, what are you specifically interested in? L2 issues? L3 issues? Routing? Or applications and related protocols? Beyond pointing to very general material such as the above, it is hard to help until you narrow your scope a little ;)
A nice repository of some of the key papers in WSNs is provided by Matt Welsh's (now slightly dated) course notes for his course at Harvard. One great aspect of this selection is that it emphasises systems that were really deployed rather than just simulated in MATLAB.
Probably you will find useful our paper https://www.researchgate.net/publication/267210410_An_Overview_of_Wireless_Sensor_Networks_Towards_the_Realization_of_Cooperative_Healthcare_and_Environmental_Monitoring
as a starting point for more references on the topic.
Chapter An Overview of Wireless Sensor Networks: Towards the Realiza...
WSN is not a cup of tea. You need to be a specific, on which layer you are interested. You will be confuse if you real any survey paper as there are many and all are lengthy.
Be specific means, you are looking for a survey paper on MAC layer of WSN, routing layer side survey paper, security issue, transport layer or what?
You have to decide about the objective of ur work on WSN once after reading the basics of WSN. For ex, if the objective is to energy reduction then u have to learn techniques for reducing energy consumption like routing, scheduling, CSIP and so on..Then you have to fix one technique and you have to make survey on different proposed work abt one technique...All the Best.