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4. NR system radio frame format
I recently learned the principles of communication, from communication principles to wireless communication principles, from 2G GSM system to 5G NR system, and I am going to do a series of documents to organize the evolution of 2G to 5G systems. The characteristics and shortcomings of each generation of communication, why it evolved, what technology was used, what problems were solved, and so on.
Young man, there is a long way to go!
This article starts with the multiple access method and modulation method.
If you don't know about modulation technology and multiple access technology, you can read the previous article:
Talk about "multiple access technology" and "modulation technology" - Zimoji's blog - CSDN Blog
| standard |
multiple access |
Modulation method (maximum) |
radio frame format |
| GSM |
FDMA+TDMA |
GMSK |
Frame (8 time slots, 4.615ms) - Multiframe (26 frames for business, 51 frames for control) - Superframe (26*51 frames) - Jumbo frame (2048 superframes) |
| WCDMA |
CDMA |
32QAM |
Each frame is 10ms long, each frame has 15 time slots, and each time slot has 2560 chips. |
| LTE |
OFDMA |
256QAM |
The frame length is 10ms, and each frame contains 10 subframes and 20 time slots; the frame structures of TDD-LTE and FDD-LTE are different |
| NR |
OFDMA |
1024QAM |
The wavelength is 10ms, divided into 10 subframes of 1ms. The subframe wave interval is variable, and the number of symbols included in the subframe is also variable. The OFDM Numberology configuration is represented by μ, which includes a set of OFDM basic parameters. |
1. GSM radio frame format
The transmission unit of the GSM system on the wireless path is a burst composed of bits modulated by GMSK, which is called a burst burst. The burst length is 156.25bit, occupying 200kHz spectrum resources. Bursts are sent over a window of time and frequency called a "time slot" - a time slot .
The burst pulse sequence is divided into 5 types. We take the ordinary burst pulse sequence as an example to illustrate:
| tail bit |
Encrypted bit |
Flag |
Training sequence |
Flag |
Encrypted bit |
tail bit |
Guard interval |
The meaning of each representative is no longer expanded, and those who are interested can consult relevant information. With the concept of time slots, we continue to talk about TDMA frames.
In the TDMA of the GSM system, each carrier frequency is defined as a TDMA frame , and each frame contains 8 time slots (TS0-TS7). The TDMA frame number needs to be defined, and the nature of the carrier can be distinguished according to the frame number.
26-frame multiframe : contains 26 TDMA frames with a duration of 120ms, generally used for TCH (Traffic CHannel service channel), as a voice channel and its associated control channel.
51-frame multiframe : Contains 51 TDMA frames with a duration of 235.385ms. This multiframe is used to carry BCH (Broadcast CHannel) and CCCH (Common Control CHannel), which are dedicated to control channels.
Superframe : accommodates 26-frame multiframes and 51-frame multiframes (note that 26 and 51 have no common divisor), and the superframe tail is 26*51=1326 frames, which is equivalent to 6.12s.
Jumbo frame : A jumbo frame contains 2048 superframe structures. Duration 3h28min53s760ms.
The relationship diagram is as follows:
2. WCDMA radio frame format
In the wireless interface of WCDMA, in terms of different protocol levels, the channels that bear various services of users are divided into three categories: physical channels, bearer channels, and logical channels. Most channels are composed of radio frames and time slots, and each radio frame contains 15 time slots.
Up channel:
Downstream channel:
3. LTE radio frame format
Each frame is 10ms long, and each frame contains 10 subframes and 20 time slots. Each time slot may have several resource block PRBs, and each PRB contains multiple subcarriers.
FDD-LTE：
TDD-LTE：
TDD-LTE has special subframes, including DwPTS, GP, UpPTS, and uplink and downlink transition points.
DwPTS: Downlink Pilot Time Slot
UpPTS: Uplink Pilot Time Slot
GP: Guard Period, corresponding to 1~10 symbols according to the length of DwPTS and UpPTS. Later evolved into CP - cyclic prefix.
Ts = 1 / (15000*2048) (S)
4. NR system radio frame format
A radio frame is 10ms long, divided into two half frames (#0~#4, #5~#9), 10 subframes, and each subframe is 1ms.
In the 4G-LTE system, the sub-carrier spacing is fixed at 15 kHz, while in the 5G NR system, the sub-carrier spacing is 15 kHz, 30 kHz, 60 kHz, 120 kHz, and 240 kHz. .
In the next issue, we will continue to introduce the sampling frequencies of these formats .