THE BASIC CONCEPT OF WiFi
The WiFi network is a technology for transmission over radio waves according to the IEEE 802.11x standard (IEEE 802.11 is a set of standard techniques of this connection technology as Wifi Alliance - http://www.wifi.org - regulations).
The WiFi network uses 02 main bands: 2.4GHz and 5GHz. This is 02 ice frequency uncensed, meaning the band is not licensed exclusively for individuals or organizations - everyone is allowed to buy, install and use WiFi (unlike the 900/1800/ band; 2100 is subject to state-specific regulations for mobile information, unlicensed organizations or individuals will not be allowed).
WiFi has many different standards, corresponding to 02 bands:
- 2.4GHz standard: 802.11 b/g/n;
- 5GHz standard: 802.11 a/n/ac.
The higher the terminal and the WiFi transmitter support (new standard), the higher the data download speed.
When investing in terminal devices (phones, computers, etc.) or WiFi transmitters, users should pay more attention to the above parameters so that they can compare and evaluate the features between products. For example:
check if the device supports the 5GHz band;
for each band, what standard does WiFi support (2.4GHz should be 802.11n, 5GHz should be 802.11ac)?
WiFi modem with MIMO support - multiple transceiver antennas?
WiFi SPECIFICATIONS
Frequency and channel width
WiFi supports flexible channel widths: 20MHz, 40MHz and 80MHz (5GHz). The larger the channel width, the higher the data transmission speed.
The 2.4GHz band has 14 frequency channels, with a channel width of 20MHz. In order not to overlap, only 3 channels can be used at one location at the same time. Details as illustrated: if the device uses channel 1, in order to avoid interference, only use channels 6 and 11.
The 5GHz band with 20MHz channel width can use 25 different channels without overlapping. If 40MHz and 80MHz channel widths are used, respectively, only 12 and 6 channels remain without overlapping.
Note:
Each country has different regulations on the power and frequencies for WiFi, so devices in some countries will not be allowed to use all 25 frequencies above. For example, in China, the frequency band from 100 to 144 is used for military purposes, so devices from China will not be allowed to use WiFi on these frequency channels.
COMPARING WiFi AND LTE (4G)
These two systems have similarities when they use OFDM modulation and support flexible frequency channel width (20MHz, 40MHz, etc.).
However, LTE is superior with regards to the resource allocation mode, which makes LTE suitable for providing large area services with many connected customers (mobile network), while WiFi is only suitable for use in small areas with few people (households, offices, etc.).
Technology | WiFi | LTE |
Support Bands
| 2.4GHz + 5GHz | 700 MHz + 1.8GHz + 2.1GHz + 2.6GHz |
Frequency channel width | 20MHz, 40MHz, 80MHz | Supports Carrier Aggreration (CA): 10MHz, 15MHz, 20MHz, 40MHz... |
Transmit power | 21~23 dBm | 43 dBm |
Transmission mode
| Half-DuplexWiFi cannot transmit and receive at the same time, because only 1 frequency channel is used for both transmitting and receiving | Full-DuplexLTE uses 2 different DL and UL frequencies, so users can download and upload data at the same time. |
| CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance): To avoid line conflicts, at a time WiFi only serves 1 client (transmitter or receiver) and this client will use the entire frequency resource (20MHz) of WiFi. After the end of data exchange, WiFi will serve another client, depending on which client's request for resource allocation is received first.
| OFDMA (Orthogonal Frequency Division Multiple Access) With the same 20MHz bandwidth as WiFi, LTE will be divided into small blocks (Resource block – RB: 180kHz) combined with a scheduling algorithm so that at a time there are always many people using the same part (RB). ) of the resource (depending on the user's needs and quality of the line).
|
Modulation and Coding Scheme | 64-QAM |
|
Feature | MIMO | MIMO* |
Comparing indoor WiFi devices of households with WiFi Hotspot devices
Popular WiFi devices on the market:
only support the 2.4GHz band, only a few devices support the 5GHz band;
in addition to dedicated WiFi devices, the WiFi hotspot mode from phones and computers usually only supports 2.4GHz; because there are few channels and many devices use it, the quality of the WiFi waves on the 2.4GHz band is very poor - this is the reason why in densely populated areas like restaurants WiFi networks are often interfered with, making them difficult to access and having low speed;
the image of 2.4GHz WiFi band in a building: there are many 2.4GHz WiFi transmitters which lead to interference and low download speed; meanwhile, almost no devices use the 5GHz band, except for the WiFi hotspot system.
WiFi hotspot devices
The main features that makes WiFi better than common WiFi devices are:
supports the simultaneous transmission of 2.4GHz and 5GHz bands;
supports the latest WiFi technology (5GHz - 802.11ac, 2x2 MIMO);
features automatic frequency channel change when detecting high noise (SINR);
supports the connection of many users at the same time (a recorded maximum of 345 users connected);
for new smartphones (Iphone 6, Samsung Note 4 and above) that support the 802.11ac WiFi standard when using WiFi, it can achieve actual download/upload speeds up to 200~220Mbps.
Please have a look below at a screenshot of some test results on Note 4 through the WiFi system:
