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Currently available WLAN products are able to provide a MAC throughput of up to 170Mbps using next-generation WLAN technologies according to IEEE standard 802.11n. The recently formed IEEE Very High Throughput (VHT) study group intends to enhance WLANs to provide Gigabit capacity in two frequency bands: (i) higher-60 GHz frequency band, and (ii) under-6 GHz frequency band. It is worthwhile to note that the higher-60GHz frequency band has a lot of unused spectrum available which can be used to provide very high speed connections. At the downside, it suffers from more obstruction difficulties and drawbacks. On the other hand, the under-6GHz frequency band has less available spectrum but it is able to be uses as a multi-user technology for improving the overall network performance since it provides backward compatibility with existing IEEE 802.11 WLAN legacy standards.
The VHT standard aims at roaming high-throughput users in a seamless manner in addition to maintaining full support of network security and management. Moreover, VHT WLANs must be backward compatible with WLAN IEEE 802.11 legacy standards. Improving the MAC efficiency, extending communication ranges, and increasing network throughput are the main enhanced properties of VHT WLANs that are considered by the VHT study group.
So far, MAC enhancements of next-generation WLANs, e.g., frame aggregation, are taken into account to improve the MAC efficiency of VHT WLANs. In addition, using multi-channel access protocols seems interesting due to their ability of providing higher MAC throughput than single channel protocols. Spatial multiplexing (in higher degrees) and cross polarized multiplexing techniques are considered to be applied at the PHY layer of VHT WLANs. Also, different digital baseband improvement approaches are intended to be used, e.g., larger constellation sizes, advanced channel coding strategies, and effective use of channel feedback methods. Increasing the symbol time is another method which has been considered to increase the throughput of VHT WLANs. Typically, the lower and higher frequency bands are applied for lower and higher throughput, respectively. The VHT study group focuses on extending the range for the lower frequencies, while the throughput extension is considered for the higher frequencies.
Typically, access points work in a serial manner with associated users sharing the network bandwidth. Applying serial transmission in VHT WLANs limits the total network throughput to 500 Mbps. Instead, by using parallelized multiplexing techniques a network throughput of up to 500 Mbps per user can be achieved.
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