Advances in MIMO Techniques for Mobile Communications—A Survey <s> IEEE 802.16 WiMAX <s> Tremendous consumer interest in multimedia applications is fueling the need for successively higher data rates in wireless networks. Data rates in wireless wide area networks are limited by the need to address wide coverage, vehicular mobility, and the limitations of licensed spectrum. Thus, data rates in WWANs continue to lag advances in wireless local area networks by orders of magnitude. There are valuable lessons to be learned from the design of WLANs that provide data rates in excess of hundreds of megabits per second. Several technologies are instrumental in enabling the future of high-performance WWANs, including multiple transmit and receive antennas, OFDM, closed loop transmission control, and low-latency MAC operation. We describe a MIMO WLAN design and prototype that exploits these attributes to provide data rates in excess of 200 Mb/s above the MAC <s> BIB001 </s> Advances in MIMO Techniques for Mobile Communications—A Survey <s> IEEE 802.16 WiMAX <s> Tremendous interest in multimedia applications such as wireless video streaming drives the need for high throughput WLAN communications. Spatial multiplexing and diversity techniques (such as space-time coding and delay diversity) are adopted in the IEEE 802.11n draft specification to fully exploit the benefit of MIMO channel. In this paper, we propose an efficient and simple algorithm that switches between these modes based on the instantaneous channel state information. The post- detection constellation-coding SNR is calculated at the receiver for each mode and is used to derive the switching criterion. The algorithm is designed for practical 802.11n systems with linear receiver and outer forward error correction codes, and does not require complicated eigen-decomposition. Simulations demonstrate the effectiveness of our switching algorithm. <s> BIB002
The IEEE 802.16 worldwide interoperability for microwave access (WiMAX) is a recently developed wireless MAN standard that employs MIMO spatial multiplexing and diversity techniques. In addition to fixed WiMAX, the IEEE 802.16e Mobile WiMAX standard has also been developed and was approved in December 2005 [14] . Fixed WiMAX networks have already been deployed around the world and Mobile WiMAX deployments have also started. 802.16e-2005 is basically an amendment to the 802. standard for fixed WiMAX with addition of new features to support mobility. 802.16e specifies the 2-6 GHz frequency band for mobile applications and the 2-11 GHz band for fixed applications (The single-carrier WirelessMAN-SC PHY specification for fixed wireless access however specifies the 10-66 GHz frequency band  .). It also specifies a license-exempt band between 5-6 GHz. A cellular network structure is specified with support for handoffs and mobile users moving at vehicular speeds are also supported, thus enabling mobile wireless internet access [14,  . In addition to single carrier transmission, the standard specifies OFDM transmission scheme with 128, 256, 512, 1024 or 2048 subcarriers. Both TDD and FDD duplexing is specified while the multiplexing/multiple access schemes include OFDMA in addition to burst TDM/ TDMA. However, scalable OFDMA is specified in all mobile WiMAX profiles as the physical layer multiple access technique. The various channel bandwidths specified in the standard include 1.25, 1.75, 3.5, 5, 7, 10, 8.75, 10, 14 and 15 MHz. WiMAX supports adaptive modulation and coding schemes. The supported modulation schemes include BPSK, QPSK, 16-QAM and 64-QAM [14,  . Optional 256-QAM support is provided in the WirelessMAN-SCa PHY  . Convolutional codes at rate1/2, 2/3, 3/4 or 5/6 are specified as mandatory for both uplink and downlink. In addition, convolutional turbo codes, repetition codes, LDPC and concatenated Reed-Solomon convolutional code (RS-CC) are specified as optional. The supported data rates range from 1 Mb/s to 75 Mb/s [14,  . IEEE 802.16e supports both open-loop and closedloop MIMO. Open-loop MIMO techniques include spatial multiplexing (SM) and space-time coding (STC) [14,   . 802.16e includes support for up to four spatial streams and therefore a maximum of 4 u 4 MIMO configuration [14,  . STC is based on the Alamouti scheme (also STBC) and is also called space-time transmit diversity (STTD). It is an optional feature and may be used to provide higher order transmit diversity on the downlink [14] . In closed-loop MIMO, full or partial CSI is available at the transmitter through feedback. Eigenvector steering is employed to approach full capacity of the MIMO channel and water filling can be used to maximize throughput by allocating power in an optimal manner BIB002 BIB001 . IEEE 802.16e supports closed-loop MIMO precoding for SM and also closed-loop STC [14,  . However, closed-loop MIMO is not yet supported in the latest WiMAX Forum Wave 2 profiles  . Another MIMO mode called "collaborative spatial multiplexing" is also specified where two subscriber stations (SS), each having a single antenna, use the same subchannel for uplink transmission in order to increase the throughput [14,    . The adaptive antenna systems (AAS) supported in 802.16e also include closed-loop adaptive beamforming, which uses feedback from the SS to the base station (BS) to optimize the downlink transmission [14,   . IEEE 802.16 Task Group m (TGm) has also been set up to develop the IEEE 802.16m standard which will enable interoperability between WiMAX and 3GPP's Long Term Evolution (LTE) standard for next generation mobile communications   . 802.16m is expected to support high-speed mobile wireless access (up to 350 km/h) and peak data rates of over 300 Mb/s using 4 u 4 MIMO  .