MO mode is adapted according to CQI reports from the MS, while considering system parameters such as number of users, ACK/NACK, CQI variation, preferred MIMO feedback mode, etc. In the uplink direction, the serving BS may adapt the MCS level based on the uplink channel quality estimation, allocated resource size, and the maximum transmission power of the MS. The transmit power of the uplink control channels (excluding initial ranging channel) is adapted according to power control commands. 10.4 MULTI-ANTENNA TRANSMISSION SCHEMES Design of mobile broadband wireless communication systems capable of data transmission rates in the excess of 1 Gbps has been of practical interest in the past decade to enable the 4th generation of cellular systems and IMT-Advanced. The use of multiple antennas at transmitter and/or receiver, 10.4 Multi-antenna transmission schemes commonly known as the Multiple-Input Multiple-Output (MIMO) system has become a pragmatic and cost-effective approach that offers substantial gain in making 1 Gbps wireless links a reality. This section provides an overview of MIMO wireless technology, including channel models, performance limits, coding, and transceiver design. MIMO techniques can increase system throughput and transmission reliability without increasing the required bandwidth. While most communication systems suffer from multi-path channels, a MIMO system benefits from the prop- agation over different paths through which the signals arrive at the receiver. A MIMO system typically performs better in an indoor environment, while it may not properly perform in Line-of- Sight (LoS) environments. The performance improvements resulting from the use of multi-antenna systems are mainly due to array gain, diversity gain, spatial multiplexing gain, and interference reduction that may be achieved through the appropriate MIMO configurations. The main advantages of multi-antenna techniques can be summarized as follows [15,41]: Array gain can be achieved through signal processing at the transmitter and/or