The field of millimeter wave has always been like a wild land in the era of 1G to 4G, which it is fertile but also thorny at the same time. It is the goal of 5G to conquer. Millimeter wave can lead 5G to reach the established peak rate, and it is also irreplaceable in terms of reducing latency.
Millimeter wave generally refers to the radio frequency spectrum in the range of 30GHz to 300GHz. Compared with the traditional wireless frequency spectrum, the frequency is much higher, so it is also called high frequency. According to the formula of "wavelength = speed of light ÷ frequency" of electromagnetic waves, the wavelength of this section of the spectrum is between 1 millimeter and 10 millimeters, which is the origin of millimeter waves. The actual millimeter wave in 5G is between 24GHz and 100GHz. The bandwidth of millimeter wave is very large, and each operator has a bandwidth of 800 MHz or even 1 GHz. With more spectrum resources, it is like a wider road, unimpeded, and the network speed will naturally be faster. Calculated according to the millimeter wave 800MHz bandwidth, the peak cell rate has reached 13Gbps, plus the 7Gbps of the 100MHz bandwidth on Sub6G, the total rate has reached 20Gbps, and the vision of 5G enhanced mobile broadband has been achieved!
5G adopts OFDM technology, which divides the carrier bandwidth into subcarriers and divides the time into time slots at the same time. The two dimensions of subcarriers and time slots are used to transmit data. The sub-carrier width is inversely proportional to the length of the time slot. The sub-carrier spacing used by millimeter waves is much wider than that of Sub6G, generally 120KHz. Therefore, the length of each time slot can be very short, 0.125ms, which is only a quarter of Sub6G (commonly used 30KHz sub-carriers). 5G uses time slots as the unit to schedule data. The shorter the time slot length, the smaller the latency of 5G at the physical layer. In this way, the millimeter wave delay in 5G is only a quarter of that of Sub6G, and the low delay requirement of 5G can also be solved!