Can user experience design (UXD) and user centered design (UCD) be considered the same?
If not, how do they relate to each other and how do they differ?
First define UXD and UCD ;-)
And since, in my experience, if you get four UX folk in a room you'll end up with eight different definitions it's hard to give an answer that will please everybody.
I've seen definitions that would make them roughly equivalent.
I've seen UXD described as a generic umbrella term, with UCD being a specific instance of a process for doing UCD.
I've seen UXD described very narrowly, with it fitting in as part of a broader UCD process.
Swings. Roundabouts. Roundabouts. Swings.
My answer from the gut would be "It doesn't matter." Pick any definition you like. The particular names we pick don't help us build better products.
UXD describes what's designed (the experience). UCD describes the process (starting with user research and validated through artefacts like personas). In practice, most UX designers try to work in a user-centered way, but that's not always easy to achieve under commercial constraints, especially when the user and the customer are not actually the same person (e.g. advertising products).
UCD ∈ UX
Put another way, user-centred design is a method (or process) to achieving good user experience.
Here is an example UCD design flow using SAP (note arrows indicating a process):
Source: SAP Design Guild