compatibility and interoperability with their legacy base standards (e.g., IEEE 802.16e-2005 was not backward compatible with IEEE 802.16-2004). Table 1-4 provides some useful information on the evolution of the IEEE 802.16 standards (already released or under development by the IEEE 802.16 Working Group as of September 2010) with hyperlinks to additional information sources. The IEEE 802.16-2009 standard is the second revision of the IEEE 802.16 standard (the first revision was released as IEEE Std. 802.16-2004) that encompasses the previous amendments and corrigenda released by this working group. This revision serves as the base standard for IEEE 02.16m, the advanced air interface, which is currently under development in the IEEE 802.16 Working Group whose release is expected in March 2011. The IEEE 802.16-2009 standard [8] contains some feature enhancements relative to the IEEE 802.16e-2005, including Frequency Division Duplex (FDD) mode enablement and bug fixes, Half- Duplex FDD terminal operation, persistent scheduling, support of 20 MHz bandwidth, improved multi-antenna transmission and processing schemes, and enhancement of multicast and broadcast services, multi-radio coexistence, location-based services, as well as load balancing. The use of complementary grouping of the mobile stations and use of two resource allocation medium access protocols per radio frame resulted in higher VoIP capacity and lower airlink transmission latency. Relaying and cooperative communication have emerged as important research topics in wireless communication in the past few years to improve performance and coverage of wireless links. In May 2006, the IEEE 802.16 Working Group assigned a task group to incorporate relay capabilities in the IEEE 802.16e-2005 air interface standard. The IEEE 802.16j task group finalized the multi-hop relay specification in 2009. Although this amendment is fully compatible with 802.16e-2005 mobile stations over the access link (i.e., the link between the relay and mobile stations), an IEEE 802.16