Some points from 802.16-2004 draft:
For cellular and multiple access channels, the uplink and downlink transmit/receive specifications are different, which is in contrast to point to point standards such as 802.11.
The PHY has four different versions:
1. WirelessMAN-SC PHY: Single carrier , targetted for 10 to 66 Ghz range
2. WirelessMAN-SCa PHY: Single carrier, Non Line of Sight operation possible, below 11 Ghz
3. WirelessMAN-OFDM PHY: Based on OFDM, Non Line of Sight operation possible, below 11Ghz
4. WirelessMAN-OFDMA PHY
I am not sure as of now if a device can support multiple PHYs or if base station (BS) can serve subscriber stations (SS) with different types of PHYs. .
However Mobile multihop relays(MMR) are supported only in the OFDMA type of PHY.
Some points from 802.16j draft:
Relay routing and channel allocation is performed at the MAC layer. Section 6.3.28 in 802.16j draft deals with this issue. Relays can be of following 4 types:
1. Transparent
2. Non transparent centralized scheduling and security
3. Non transparent decentralized scheduling and centralized security
4. Non transperant decentralized scheduling and security.
A transparent relay is one where the SS is oblivious to the presence of intermediate relay
A non transparent relay is the one where the SS knows about the presence of intermediate relay
Scheduling refers to channel allocation where as decentralized security refers to the fact that a relay is non regenerative decode and forward type.
Routing decisions are taken centrally by the base station. Algorithm for optimal path selection is beyond the scope of the standard. (There is a room for applying our creativity here).
Here is a cool paper that I found. It was preetty useful:
http://www.fujitsu.com/downloads/MAG/vol44-3/paper10.pdf
