Cooperative principles in Wimax

Cooperative diversity is an important type of cooperation that is useful in wireless networks. Although the purpose of employing relays is different i.e. to increase cell coverage and also help mobile stations (MS) to save power, there is an additional adavantage of being able to exploit spatial diversity from the multiple relay paths created.
Aside: Spatial diversity can be simplistically explained as the advantage that a receiver gets when he "sees" multiple copies of the incoming signal. Imagine the advantage that we have when we see with two eyes as compared to a scenario if humans had only a single eye (God forbid!).

The idea of wireless relay first originated as an information theoretical scenario in Cover and Gamal (1979). Some of the important research in this area is listed below: (Source: Wimax Evolution: Emerging technologies and applications: Wiley 2009)
1. The relay channel (Cover and Gamal (1979))
2. User cooperative diversity (Sendonaris et al.(1998))
3. Cooperative coding (Hunter and Nosratinia(2002))
4. parallel relay channel (Gastpar et al.(2002))
5. Multihop diversity (Boyer et al.(2004), Gupta and Kumar (2003))

A few of the practical scheduling issues in a wireless network are:
1. Which entities make the cooperation decision (Always a BS in the case of Wimax)
2. Whether to relay or not
3. How to relay the data (different cooperative diversity scheme)

Relay selection method is not specified in the current 802.16j draft. Ideally a decision should be made based on the CSI and the number of hops (delay constraint at the receiver). I would like to learn more about relay selection algorithms. It is quite obvious that as the network scales in size, this algorithm will become more and more complicated. The question is: Is there a sub optimal way which is also practically feasible for relay selection? A million dollar question....comments and suggestions are welcome.. :)