Has anyone used LORA's SX127x chip? What exactly is spread spectrum? What's its significance?

天涯海角sr

Has anyone used LORA's SX127x chip? What exactly is spread spectrum? What's its significance? [Copy link]

After reading some official explanations, it is nothing more than combining the original transmission time of 1 bit with a higher frequency code. But what is the meaning of this? The signal transmission of this channel is not accelerated.

chunyang

The original poster has misunderstood. Spread spectrum is the expansion of the signal spectrum, not time and code.

chunyang

Signal transmission is essentially energy transmission. Compared with non-spread spectrum, spread spectrum expands the spectrum of energy distribution. Its biggest advantage is that it reduces the possibility of interference with a certain frequency/segment in the spectrum. When a large number of same-frequency and near-frequency signals are transmitted at the same time, the same-frequency and near-frequency signals will interfere with each other. After spectrum expansion, the energy distribution per unit frequency band is greatly reduced under the same transmission power, that is, the same energy output. This is equivalent to a decrease in background noise, which has a positive significance for improving the signal-to-noise ratio. If in an absolutely clean electromagnetic environment without interference, spread spectrum has no advantage over non-spread spectrum. But in reality, the more commonly used communication frequencies are, the heavier the interference is, and the significance of spread spectrum becomes more apparent at this time.

天涯海角sr

FHSS: Frequency Hopping Spread Spectrum Technology Frequency Hopping: Utilize the entire bandwidth (spectrum) and divide it into smaller sub-channels. The sender and receiver work on each channel for a period of time and then move to another channel. In layman's terms, LoRa wireless transmission works on multiple frequency bands. When sending and receiving signals, it also jumps on multiple frequency bands. If there is an abnormal communication in one frequency band, it jumps to an adjacent frequency band to continue communication. The advantage of frequency hopping communication is that the channel is not unique, and even if there is an abnormality in a frequency band, it will not affect normal communication. Spread spectrum: It uses more than 10 chips to represent the original "1" or "0" bit, so that the original higher power and narrower frequency becomes a lower power frequency with a wider bandwidth. Generally speaking, the digital signal "1" or "0" is encoded and represented by n chips, and spread spectrum is based on this encoding and the chips are lengthened. For example, n chips represent a digital "1". After spread spectrum, 2n (2n is taken at random and is determined by the spread spectrum factor) chips are used to represent a digital "1". The advantage of this is that the anti-interference ability to noise becomes stronger, that is, the signal-to-noise ratio is higher. This is one of the reasons why LoRa can communicate over long distances. The disadvantage is that the transmission rate is reduced. The truth is that LoRa trades the transmission rate for the communication distance. BW: Spread spectrum modulation bandwidth The bandwidth also indicates the transmission rate. The bandwidth here refers to the bandwidth, that is, the frequency width of the frequency band, which determines the upper and lower frequencies of the center frequency. For example, if the center frequency is 433MHZ and the bandwidth is 2MHZ, the frequency of the communication spectrum (channel) is 432MHZ~434MHZ. SF: Spread spectrum factor is used for spread spectrum settings. The larger the spread spectrum factor, the higher the signal-to-noise ratio and the lower the transmission rate. The above is part of the data of SX127x series wireless communication: 1. Does not spread spectrum mean that information is only sent at the center frequency (433MHz)? 2. Spread spectrum means that the same signal is transmitted at various frequencies within the BW range of the center frequency? Or does it mean that it finds which segment within the BW range has no interference and then only selects this frequency segment to send? 3. Is the chip rate generally fixed? So the larger the spread spectrum, the slower the transmission?

懒猫爱飞

Tianya Haijiao sr posted on 2018-8-31 14:13 FHSS: Frequency Hopping Spread Spectrum Technology Frequency Hopping: Utilizes the entire bandwidth (spectrum) and divides it into smaller sub-channels. The sender and receiver on each channel...

This is really a learning experience

DNSJ233

As an IC supplier for 19 years, we have long-term stock supply of Nordic, TI, and Espressif brand chips. We also have long-term stock supply of SX series chips and modules.