Advances in MIMO Techniques for Mobile Communications—A Survey <s> IEEE 802.11n Wi-Fi <s> We present an overview of the MAC and PHY layer enhancements required to ensure high application layer throughput for IEEE 802.11n. We describe an enhanced scheduled mode operation which is shown, through simulation, to yield an application layer throughput that is greater than 100 Mb/s in practical scenarios. We also demonstrate that the proposed enhancements significantly improve the application layer throughput with EDCA. <s> BIB001 </s> Advances in MIMO Techniques for Mobile Communications—A Survey <s> IEEE 802.11n Wi-Fi <s> This paper presents a high throughput, parallel, scalable and irregular LDPC coding and decoding system hardware implementation that supports twelve combinations of block lengths 648, 1296, 1944 bits and code rates 1/2, 2/3, 3/4, 5/6 based on IEEE 802.11n standard. Based on architecture-aware LDPC codes, we propose an efficient joint LDPC coding and decoding hardware architecture. The prototype architecture is being implemented on FPGA and tested over the air on our wireless OFDM testbed, which is a highly capable, scalable and extensible platform for advanced wireless research. The ASIC resource requirements of the decoder are reported and a trade-off between pipelined and non-pipelined implementation is described. <s> BIB002 </s> Advances in MIMO Techniques for Mobile Communications—A Survey <s> IEEE 802.11n Wi-Fi <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> BIB003 </s> Advances in MIMO Techniques for Mobile Communications—A Survey <s> IEEE 802.11n Wi-Fi <s> This paper analyzes the impact of different MAC (medium access control) and transmission rate adaptation schemes on wireless mesh networks. The considered protocols include three different MAC protocols specified in IEEE 802.11 standards, i.e., 802.11, 802.11e, and 802.11n, and three rate adaptation schemes, i.e., ARF (automatic rate fallback), RBAR (receiver-based auto rate), and 802.11n rate adaptation. We also study the interactions of these MAC strategies with the state-of-the-art routing metric ETT (expected transmission time). Through comparative simulation evaluations, we investigate the effectiveness of these protocols when they coexist on both single-hop and multi-hop wireless mesh network environments. As these MAC strategies are designed for single-hop WLANs, we observed their limitations on multi-hop wireless mesh networks. We analyze their performances and suggest solutions for improvements. Based on our simulation results, we also argue for the need of a new routing metric that takes advantage of the new emerging MAC features. <s> BIB004
The IEEE 802.11n WLAN standard incorporates MIMO-OFDM as a compulsory feature to enhance data rate. Initial target was to achieve data rates in excess of 100 Mb/s  . However, current WLAN devices based on 802.11n Draft 2.0 are capable of achieving throughput up to 300 Mb/s utilizing two spatial streams in a 40 MHz channel in the 5 GHz band  . Initially, there were two main proposals one form the WWiSE consortium and the other from the TGnSync consortium competing for adoption by the IEEE 802.11 TGn. However, another proposal by the Enhanced Wireless Consortium (EWC) was finally accepted as the first draft for IEEE 802.11n  . The IEEE 802.11n standard proposes the use of the legacy 20 MHz channel and also an optional 40 MHz channel. The available modulation schemes include BPSK, QPSK, 16-QAM and 64-QAM   . Convolutional coding with different code rates is specified and use of low-density parity-check (LDPC) codes is also supported  BIB002 . The MIMO techniques adopted include both spatial multiplexing and diversity techniques. Open-loop MIMO (OL-MIMO) techniques which do not require channel state information (CSI) at the transmitter seem to have been preferred BIB003 . Non-iterative linear minimum mean square error (LMMSE) detection has primarily been considered so as to minimize the complexity associated with MIMO detection while ensuring reasonably good performance  . Spatial spreading mentioned in BIB001 is an open-loop MIMO spatial multiplexing technique where multiple data streams are transmitted such that the diversity is maximized for each of the streams. The MIMO diversity techniques introduced in the standard include space-time block coding (STBC) and cyclic shift diversity (CSD) which extend the range and reception of 802.11n devices. In addition, conventional receiver spatial diversity techniques like maximum ratio combining (MRC) are also specified. Transmit beamforming is also specified as an optional feature  . The Cisco Aironet 1250 series access point based on 802.11n draft 2.0 supports open-loop transmit beamforming  . 802.11n draft 2.0 specifies a maximum of 4 spatial streams per channel. Thus, a maximum throughput of 600 Mb/s can be achieved by using 4 spatial streams in a 40 MHz channel. In addition to spatial multiplexing and doubled channel bandwidth, more efficient OFDM with shorter guard interval (GI) and new medium access control (MAC) layer enhancements (e.g. closed-loop rate adaptation BIB004 ) have also contributed to the increased throughput of 802.11n  .