IEEE 802.11n/ac Data Rates under Power Constraints

IEEE 802.11n/ac are two recent enhancements that increase the data rates of WLANs significantly thanks to the use of channel bonding, spatial multiplexing, an additional short guard interval, and new modulation and coding schemes. They offer a maximum transmission rate of 600 Mbps for 802.11n and 7 Gbps for 802.11ac. Due to regulatory power constraints, the sender may be obliged to divide its transmission power over different sub-channels and spatial streams. This allows the sender to respect the regulatory requirements but reduces the range of wide channels and multiple streams compared to narrow channels and single stream. Besides, the use of spatial multiplexing does not allow the receiver to take a full advantage of the diversity gain. This is another factor that reduces the range of Multiple Input Multiple Output (MIMO) transmissions. So increasing the channel width and the number of spatial streams reduces the communication range significantly. Therefore, legacy 20 MHz channels with a single stream transmission may offer higher throughput than wide channels with multiple spatial streams. This affects the performance of rate adaptation algorithms. In this paper we introduce the power constraints that should be respected in WLANs and their impact on the range of 802.11n/ac data rates. We show that increasing the channel width and the number of spatial streams reduces the transmission range. Then we define a rate ordering scheme that selects the best data rates among those available. Our scheme intends to improve most rate adaptation algorithms, such as MinstrelHT. Finally we show, using simulation that our method enhances the throughput and the stability of MinstrelHT.