| In recent years, there has been a rapid growth in the deployment of wireless local area networks (WLAN). Standards 802.11a and 802.11b depict the standards for WLAN implementations in the 5 GHz and 2.4 GHz bands respectively; with raw data rates up to 54 Mbps and the standards-plus techniques have achieved data rates up to 108 Mbps. With new WLAN applications, such as wireless HDTV (High Definition TeleVision) video streaming, demand higher data rates beyond those supported by 802.11g. As the WLAN industry matures, the demand for higher throughput and higher performance have spurred the adoption of link budget and spatial diversity improvement techniques into 802.11g products.So that, a high throughput task group within 802.11 was formed in 2003 to develop a new amendment to the 802.11 standard for WLAN networks that be known as IEEE802.11n Standard. This special group is called Task Group 802.11n (TGn). During the initial development of the 802.11n amendment for improving the throughput of wireless LANs, a lot of excitement existed surrounding the potential higher throughput (i.e., faster downloads), and increased range (distance) achievable. The latest draft of 802.11n (Draft 11.0) offers the potential of physical layer (PHY) data rates up to 600 Mbps. This is achieved through the use of multiple transmit and receive antennas, referred to as the combination between Multiple Inputs Multiple Outputs (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM). Using techniques such as Spatial Division Multiplexing (SDM), transmitter Beamforming, and Space-Time Block Coding (STBC), MIMO is used to increase dramatically throughput over single antenna systems (by two to four times) or to improve range of reception, depending on the environment.During nearly 1 year does research about the physical layer of 802.11n; I got knowledge of new techniques which are applied in 802.11n. In previous Standard 802.11g, the main technique is OFDM which benefits are easy to implement; using effective frequency resource and solve well with the selective fading effect. In Draft Standard 802.11n, the great advantage is MIMO technique. OFDM and MIMO techniques can be combined to achieve high spectral efficiency and increased throughput. At the transmitter, the OFDM-MIMO system transmits independent OFDM modulated data from multiple antennas simultaneously. At the receiver, after OFDM demodulation, MIMO decodes each sub-channel to extract data from all transmits antennas on all the sub-channels.Techniques can also be classified into 2 parts. The part undertakes the throughput such as constellation mapping (M_QAM), code rate, the number of spatial stream and the channel bandwidth. The part undertakes the realizable and performance such as Forward Error Correction (FEC), OFDM, STBC and Beamforming.With knowledge about physical layer in 802.11n combine with skills using Simulink of Matlab, the simulation was well done. Results of simulation show out waveforms and signals space of received signals, illustrate data rates which are depended on the performance of channel, draw curves about Bit Error Rate (BER), Packet Error Rate (PER) and Throughput in difference scenarios. Furthermore, some comparisons between results are considered and discussed to get conclusions about the performance of system. |
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