It could be that a neighbour has a new wireless router. If this is on the same channel as yours then it could interfer with your signal (default tends to be 1).
Try changing the channel on the router and see if it improves.
There are some tools oput there on tinter web that you can use to see what routers are in range and what settings they have. Could use this tio find an unused channel that is as far from others as possible
7
EDIT – Bugger what he said ^^