Use Multiple Xbee's

I want to use multiple (30 No.) Xbee’s in one network . All end device fixed in inside the each 29 rooms , coordinator device is in outside corner, connecting with computer . The problem is coordinator device is not receiving the data from end device which is fixed inside room more distance above 10 mtr. How can i boost the signal of end device ? or any other method ?
Please let me know the ans. It some urgent. Thank You

Which XBee product and firmware are you working with?

I am Using Xbee S2C Module

You never listed what firmware version you are working with.

Assuming that you are working with the Zigbee versions (405x), then first off, the Coordinator only supports up to 0x14 (20) sleeping end devices. To get more end devices, you would need to add one or more routers to your network.