Title: Wireless Communications Basics -- Calculating Router Rates [Print this page] Author: GTAC-Sophia Time: 2023-5-29 15:09 Title: Wireless Communications Basics -- Calculating Router Rates (1) Wireless rate 1. Maximum rate 54 Mbps of Wi-Fi 2/3 (802.11a/g) (single spatial stream)
(1) OFDM provides 52 subcarrier channels of which48 are used for data transmission.
—48 lanes are available out of total 52 lanes
(2) The 64-quadrature amplitude modulation (QAM)encoding mode allows every subcarrier channel to carry 6 bits of data in a transmission.
—Six seats in each vehicle in each lane
(3) In 64-QAM, 3/4 of the bits are used for transmission and the rest are used for verification.
—3/4 of the six seats are available.
(4) The time of a transmission is 4 µs.
—One vehicle leaves in each lane every 4 µs.
Therefore, the maximum rate (maximum passengers each second) of 802.11a/g is as follows:
(1s/4 µs) x (6bits x 48 x 3/4) = 54 Mbps ________________________________________ 2. Maximum rate 150 Mbps of Wi-Fi 4 (802.11n)(single spatial stream)
(1) Wi-Fi 4 has optimized OFDM to provide 56subcarrier channels of which 52 are used for data transmission.
—52 lanes are available out of total 56 lanes
(2) Wi-Fi 4 extends the operating bandwidth to 40MHz which allows more channels. The total number of subcarrier channels is increased from 56 to 112, among which 108 can be used for data transmission.
—108 lanes are available out of total 112 lanes
(3) The 64-QAM encoding mode allows every subcarrier channel to carry 6 bits of data in a transmission.
—Six seats in each vehicle in each lane
(4) Wi-Fi 4 has optimized 64-QAM to increase the percentage of data transmitted from 3/4 to 5/6.
—5/6 of the six seats are available.
(5) Wi-Fi 4 reduces the transmission time by 400 ns to 3.6 µs.
—One vehicle leaves in each laneevery 3.6 µs.
Therefore, the maximum rate (maximum passengers each second) of Wi-Fi 4 is as follows:
(1s/3.6 µs) x (6bits x 108 x 5/6) = 150 Mbps ______________________________________ 3. Maximum rate 433.33 Mbps of Wi-Fi 5 (802.11ac)(single spatial stream)
(1) Wi-Fi 5 uses OFDM optimized by Wi-Fi 4 and provides 56 subcarrier channels of which 52 are used for data transmission.
—52 lanes are available out of total56 lanes
(2) Wi-Fi 5 extends the operating bandwidth to80MHz which allows more channels. The total number of subcarrier channels is increased from 112 to 242, among which 234 can be used for data transmission.
—234 lanes are available out of total242 lanes
(3) The 256-QAM encoding mode allows every subcarrier channel to carry 8 bits of data in a transmission.
—Eight seats in each vehicle in each lane
(4) In 256-QAM, 5/6 of the bits are used for transmission and the rest are used for verification.
—5/6 of the six seats are available.
(5) The time of a transmission is 3.6 µs.
—One vehicle leaves in each lane every 3.6 µs.
Therefore, the maximum rate (maximum passengers each second) of Wi-Fi 5 is as follows:
(1s/3.6 µs) x (8 bits x 234 x 5/6) = 433.33 Mbps 4. Maximum rate 1201 Mbps of Wi-Fi 6 (802.11ax) (single spatial stream)
(1) Wi-Fi 6 adopts OFDMA and provides 242subcarrier channels on a 20-MHz-wide band, of which 234 are used for data transmission.
—234 lanes are available out of total242 lanes
(1) Wi-Fi 6 extends the operating bandwidth to 160MHz which allows more channels. The total number of subcarrier channels is increased. 980 x 2 channels can be used for data transmission.
—980 x 2 lanes are available
(2) The 1024-QAM encoding mode allows every subcarrier channel to carry 10 bits of data in a transmission.
—10 seats in each vehicle in each lane
(3) In 1024-QAM, 5/6 of the bits are used for transmission and the rest are used for verification.
—5/6 of the six seats are available.
(4) The time of a transmission is 13.6 µs.
—One vehicle leaves in each lane every 13.6 µs.
Therefore, the maximum rate (maximum passengers each second) of Wi-Fi 5 is as follows:
(1s/13.6 µs) x (10 bits x 980 x 2 x 5/6) = 1201Mbps (2) Factors affecting router rates
1. Code rate, that is, the average number of passengers in a vehicle
2. Transmission time, that is, the average interval at which one vehicle leaves in each lane
3. Bit rate mediated by modulation method, that is, the number of seats in a vehicle.
4. Bandwidth which determines the number of subcarrier channels (lanes)
5. Spatial streams. The preceding examples assume that there is only one spatial stream. The total maximum transmission rate equals the maximum rate of a single spatial stream multiplying the number of spatial streams. In Wi-Fi 4, the maximum rate of a single spatial stream is 150 Mbps. If there are four spatial streams, the total maximum rate is 600 Mbps (150 Mbps x 4).
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