Regarding Wi-Fi's new rate standard IEEE 802.11ac, from June (2012) onwards, it was launched with great fanfare. At first, only laptops and wireless routers were adopted, and then TVs (such as LG) were also adopted. Later, the top smart type Mobile phones (HTC new One, Apple iPhone 5, etc.) are also adopted. After all types of products are adopted, it is already a new technology that cannot be ignored.
Although 11ac has been gradually developed, strictly speaking, the 11ac standard has not been officially finalized. The standard that started in June 2012 is the second draft version of the technical proposal (Draft 2.0). In June 2013, one year later, The Wi-Fi Alliance officially proposed the 11ac test and verification plan, but it is still not the official version. It is only the third draft version (Draft 3.0). The official version of 11ac is based on the progress of the contract and the progress is delayed. It will not be finalized until 2014.
Wide range of technologies
The 11ac standard is the same as the rate standard 11n before 11ac. In addition to the commercialization of the proposal from the draft version, 11ac is also a wide range of technologies and contains many optional functions. Not everyone can fully realize all technical functions.
First of all, in terms of the number of antennas (strictly speaking, it will be called spatial stream in theory), the 11n standard allows the transmission and reception of up to 4 antennas, but in actual business, most operators only implement 3 groups, and even only 2 groups. . Similarly, the 11ac standard can have up to 8 groups of antennas, but 11ac products that have been implemented for one year are still dominated by 3 groups of antennas.
In addition, 11n has a bandwidth of 20MHz per channel, which is compatible with 11g in some highlands, but 40MHz can also be used to double the transmission rate. Similarly, 11ac is compatible with 20MHz of 11g and 40MHz of 11n, but 80MHz and 160MHz can be further selected to increase the transmission rate by 2 times and 4 times. Not only this, 11n sends up to 64QAM modulation, 11ac can be further modulated to 256QAM.
In addition, 11ac also has many optional functions, such as low-density parity check code (LDPC), STBC (Space-TIme Block Coding), TxBF (Transmit Beamforming), and shorter band guard interval (Short Guard Interval; SGI), that is shortened from 800nS (nanosecond) to 400nS.
Reality and ideal
It can be seen from the above description that the ultimate powerful 11ac is used by 8 groups of antennas at the same time, the channel bandwidth is 160MHz, and the 256QAM modulation is used, the code rate is 5/6, and the guard interval is 400nS. ? The current answer is no.
Due to the wide range of 11ac technology, the industry will implement it in two waves and two phases. The first phase (Wave 1) will still be mainly 80MHz, and the second phase will only adopt 160MHz. At the same time, the first phase is also based on 3 antennas In the second stage, 4 groups of antennas will be introduced.
Therefore, most of the current 11ac products only advertise transmission rates above Gbps, generally about 1.3Gbps. This data uses 3 groups of antennas, each group uses 400nS spacing, 80MHz channel bandwidth configuration, so each group of antennas 433.3 Mbps, multiplied by 3 times is about 1.3Gbps.
MU-MIMO is the main difference
It can also be seen from the above that the acceleration method of 11ac is almost the same as that of 11n, but it is more enhanced. However, one point is that 11ac is obviously different from 11n, that is, 11n only has MIMO, but 11ac has MU-MIMO (MU is MulTI- User means multiple users), can allow an 11ac router to serve two terminals at the same time, no longer can only serve one at a time.
Therefore, the so-called 11ac has a maximum of 8 antennas, and 8 of them cannot serve a single device. A single device can receive the service of up to 4 antennas. If the bandwidth of 160MHz is used, each antenna has 866.7Mbps, and 4 antennas are about 3.47Gbps This is also the transmission limit of 11ac.
In other words, if there are 4 sets of 11ac antennas in the laptop or TV, the maximum transmission rate of 3.47Gbps can be obtained, but if the number of antennas decreases, the transmission rate will also decrease. If only one Wi-Fi antenna is allowed in the mobile phone, then The transmission rate will be limited to 866.7Mbps (160MHz, 400nS), and at this stage it is mostly 433.3Mbps (80MHz, 400nS).
Does the new Apple AirPort Extreme have 6 antennas?
Finally, the recent (June 2013) Apple ’s new AirPort Extreme claims to have 6 antennas, does it mean that it already supports 11ac MU-MIMO? The answer is no. The so-called 6 groups of antennas only use 3 groups for 11n and 3 groups for 11ac, rather than 11n or 11ac, which has reached the level of 4 groups of antennas, not to mention the ultimate state of MU-MIMO.
The official version still needs to wait
Looking forward to the future, if you look at the 11n model, the official version of 11ac is probably a good thing. 11n is also commercialized from Draft 2.0. It started from the beginning of 2007 until the official version was completed in October 2009. 11 drafts. Similarly, 11ac started from Draft version 2.0 in June 2012, and then announced that the official version has been delayed. The current version is Draft 3.0. It seems that the official version still needs to wait for a while.
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