Ultra low power tree network with multiple routers

I need to make a tree network using Xbee with the lowest possible power consumption. For example, I have a coordinator, two routers and an end device. The coordinator is connected to the router, one router connected to another and the final router with the end device, like this:

C –> R –> R –> ED

The coordinator is always powered on but this is no problem; the real problem comes with the powering of the routers and the end device.
The consumption with sleep modes fulfills my requiriments, but I can’t use it on the routers, because the routers need to be awake to transmit data from the end device to the coordinator (if any of the routers is asleep, when the end device send it’s data, it cannot reach the coordinator).
For this reason I can´t save any power in the router and the idle current is just too high. Is there a way to sleep the router and wake it remotely using for example a low power rf receiver to trigger pin sleep? I would appreciate if anyone has a detailed solution to this proble,.
P.D. I can’t use cycle sleep. because when the network becomes larger (more routers) it’s just so hard to syncronize all sleep cycles from the routers and ensure that they are all awake when time for transmiting data from end devices come.

Looks like you are trying to use a Zigbee mesh based product which requires Routers to be always on.

From the sounds of it, you would be better off using the synchronous sleep functions found in the Digi Mesh versions of the XBee. This option allows for all nodes but the coordinator to sleep and wake together. Then allows the data to be sent over each of the nodes till it reaches the destination.

I checked it out and I think is a nice solution for me. Thx