Author: Chen Songlin
Since 2010, the smartphone market has grown steadily. Smartphones generally provide a wireless local area network (WLAN) connection, which provides a broad market prospect for WLAN RF units.
Since the release of the WLAN standard in 1997, in order to improve the transmission rate and throughput, the physical layer protocol has been supplemented, and new requirements have been placed on the operating frequency, performance and complexity of the radio unit.
This paper reviews the development of the WLAN standard IEEE 802.11 and judges its development trend. Combined with the new requirements for RF units in specific applications for WLANs in smartphones, NXP will provide new RF solutions that fully meet the RF requirements of the latest WLAN standards.
WLAN history and development trends
Wireless Local Area Network (WLAN) is a local area network connection based on the IEEE 802.11 standard and using free ISM band RF resources. The first version of IEEE 802.11 was developed by the IEEE in 1997, which defines the media access control layer and the physical layer. The physical layer defines the ISM band with a working frequency of 2.4 GHz, and the total data transmission rate is 2 Mb/s.
In 1999, IEEE 802.11 added two complementary versions, IEEE 802.11a and IEEE 802.11b, where IEEE 802.11a defines the ISM band at 5 GHz with a data transmission rate of 54 Mb/s; while IEEE 802.11b still operates at 2.4 GHz. ISM band, but the transmission rate can reach 11Mb/s.
In 2003, IEEE supplemented the physical layer of WLAN and released IEEE 802.11g. This version still uses the 2.4GHz band, but the transfer rate is increased to 54Mb/s.
In 2009, the IEEE renewed the physical layer and introduced IEEE 802.11n. The standard supports both 2.4GHz and 5GHz bands, and can use double bandwidth of 40MHz to support Multiple Input Multiple Output (MIMO) technology. In theory, its highest transmission rate can reach 600Mb/s (this rate must meet 64QAM modulation, 5/6 encoding rate, 40MHz channel bandwidth, 400ns guard interval, 4 spatial streams, and each stream). The rate is 150 Mb/s).
In January 2014, as an upgrade to IEEE 802.11n, the new version of IEEE 802.11ac was adopted, which uses the 5 GHz band to provide higher throughput (the rate at which data is successfully received). IEEE 802.11ac has a wider RF bandwidth (compared to the IEEE 802.11n 40MHz bandwidth, IEEE 802.11ac provides at least 80MHz, up to 160MHz bandwidth), with more MIMO space stream (up to 8 channels), and supports more downlink User Multiple Input Multiple (MU-MIMO), and more advanced 256-QAM digital modulation. Therefore, IEEE 802.11ac has a higher data transmission rate, and each stream can provide a transmission rate of up to 866.7 Mb/s in the case of 256QAM modulation, 5/6 coding rate, 160 MHz bandwidth, and 400 ns guard interval.
In addition, in order to achieve higher data throughput, the WiGig organization merged into the WiFi Alliance in 2013. WiGig is committed to the IEEE 802.11ad standard, which uses the 60 GHz band to provide short-range wireless communication services with transmission rates up to 7 Gb/s. Since the 60 GHz signal cannot penetrate the obstacle, when the terminal device enters an area that the WiGig signal cannot cover, it will automatically switch to the lower frequency band, but the transmission rate will drop drastically.
Table 1 summarizes the evolution of the IEEE 802.11 standard, from which it can be seen that every upgrade and supplement of the WLAN standard is nothing more than obtaining transmission rate/throughput. In order to achieve this goal, the following two methods can be used. 1. Adopt a wider channel bandwidth. To achieve this, it is sometimes necessary to increase the operating frequency band. As a result, WLANs have transitioned from the initial 2.4 GHz to 5 GHz, and the 60 GHz standard has emerged, allowing for wider spectrum resources. 2. Adopt spatial multiplexing technology. Beginning with IEEE 802.11n, MIMO technology was introduced into WLAN, and the maximum spatial stream was also increased in IEEE 802.11ac.
Table 1: WLAN physical layer standard evolution
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