peration at the physical layers of IEEE 802.16m and 3GPP LTE/LTE-Advanced can be better understood. The control signaling mechanisms of the legacy system have undergone a substantial change in IEEE 802.1 16m to improve reliability and coverage, and to reduce the signaling overhead and control-plane and user-plane latencies. The IEEE 802.16m system requirements called for improved link-budget in the downlink and uplink for both traffic and control channels. As a result, the use of dual transmit-antenna at the base station as a minimum configuration has been mandated. Unlike the legacy system, all downlink control channels in IEEE 802.16m use frequency-domain transmit diversity as the default multi- antenna mode of operation. The reduction in Layer 2 signaling overhead, use of more robust multi- antenna techniques along with user-dedicated precoded reference signals, and improved feedback schemes have resulted in a significant increase of VoIP and data capacity compared to the legacy system. We start with the description of the control channels and signaling mechanisms and compare them to the corresponding techniques in the legacy system, and then will proceed to detailed discussion of multi-input multi-output techniques. Similar to the previous topics, the corresponding methods in both IEEE 802.16m and 3GPP LTE/LTE-Advanced are discussed to allow the reader to draw parallels and to better understand the design philosophies in the 4th generation cellular systems. 10.1 CONTROL CHANNELS In the IEEE 802.16-2009 standard, the control signaling for downlink or uplink resource allocations and other operational aspects of the system is performed using downlink or uplink information elements included in the Medium Access Protocol (MAP) MAC management messages. The infor- mation elements of all active users in the cell, as well as broadcast messages, are jointly encoded and transmitted using a robust transmission scheme. The information elements contained in the DL or UL MAPs are distinguished using the connection identifie