LDPC Tone GI Insertion Mapper Mapper Windowing Constellation LDPC Tone GI Insertion Mapper Mapper Windowing Spatial streams Space-time streams Several transmission chains Figure 5.15. Generation of DATA field - Data unit for a single user LDPC encoder - Radio channel bandwidth of 80 + 80 MHz 5.3.2. Frequency plan The 802.11ac interface operates in the U-NII (Unlicensed-National Information Infrastructure) band at 5 GHz. Adjacent radio channels of 20 MHz are grouped in pairs to form a 40 MHz channel. Adjacent radio channels of 40 MHz are grouped in pairs to form an 80 MHz channel. Adjacent radio channels of 80 MHz are grouped in pairs to form a 160 MHz channel (Figure 5.16). It is allowed for two 802.11ac access points to select the same 80 MHz bandwidth, but one access point must have its primary channel of 20 MHz in the lower half-band, and the other access point puts its primary channel of 20 MHz in the upper half-band. Sub-band A Sub-band B Sub-band C Channel number 20 MHz 40 MHz 80 MHz 80 MHz USA and Japan only Figure 5.16. Frequency plan Channel bandwidths of 20, 40, 80 and 160 MHz 100 Wi-Fi Integration to the 4G Mobile Network The 802. 11n mobiles associated with the first access point can transmit in the lower half-band of 20 or 40 MHz, at the same time that the 802.11n mobiles associated with the second access point transmit in the upper half- band of 20 or 40 MHz. An 802.11ac mobile can transmit in the 80 MHz band if it is available. Sub-band A Sub-band B Sub-band C Channel number USA and Japan only Figure 5.17. Frequency plan Channel bandwidths of 80+80 MHz The frequency plan allows only two channels at 160 MHz. Each channel can be constrained by regulatory requirements. The aggregation of two non- contiguous channels of 80 MHz defines 13 possibilities, thus allowing greater flexibility for interference protection (Figure 5.17). 5.3.3. Frequency multiplexing For a radio channel of 20 MHz, the bandwidth is divided into 64 sub- carriers. The signal is transmitted on the sub-carriers -28 to -1 and 1 to 28,