So far we have been talking about the cross-layer design activity largely from the research literature. Interestingly, cross-layer design ideas have been making their way into several ongoing standardization activities and commercial products too. In this section we take a brief look at some of this industry activity.
The channel-dependent scheduling that we discussed in Section 6.3.2 has been incorporated into the high data rate (HDR) version of CDMA2000 (1xEV-DO) and enhanced general packet radio service (EGPRS) in the EDGE extension of GSM . In these systems, the users periodically update the base station about the state of the downlink channel. This information is used by the base station for scheduling the transmissions to the different users.
The problem of vertical handovers that we discussed in Section 6.3.3 is being addressed by the IEEE 802.21 standards group. The IEEE 802.21 group is defining standardized interfaces for sharing information from the lower layers (e.g. link layer and physical layer) with the higher layers (e.g. network layer). The IEEE 802.21 effort thus is an interesting example of convergence between the performance viewpoint, which dictates the need for cross-layer information sharing, and the architectural viewpoint, which requires standardized and well-defined interfaces between the modules.