The same frequency band, different communication methods are very different, such as ASK, FSK, FHSS, DSSS, etc., from the anti-interference ability, communication security confidentiality, reliability are different. The ZigBee system, like the CDMA system, adopts the Direct Sequence Spread Spectrum (DSSS) technology, which is a communication method with strong anti-interference ability, high confidentiality and reliability. If you have used communication products of these two technologies, you will find that there is a clear difference in reliability between the two.
Since the signal-to-noise ratio required by the spread spectrum technology in normal communication can be very low, that is to say, it can still work normally in an environment with strong interference. According to calculations and experiments, this is equivalent to an increase in its receiving sensitivity by 7dBm. It is also not easy to interfere with others. In other words, it can transmit longer distances using lower power. There are many other advantages of the direct-sequence spread spectrum technique adopted by ZigBee which will not be discussed here. Below we quote some information related to the superiority of spread spectrum technology for your reference:
CDMA is a new type of digital cellular technology launched in 1995 after the introduction of digital communication technology in the world. The outstanding advantages of wide range, low power consumption of mobile phones, and high voice quality have pushed mobile communication technology to a new stage of development. Compared with FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access) systems, CDMA (Code Division Multiple Access) cellular systems have the following outstanding advantages:
1. Good anti-jamming performance Because CDMA is processed by spread spectrum, it has good anti-jamming performance, and can coexist with the narrow band of the same frequency band without affecting its normal operation.
2. Strong anti-multipath fading ability Multipath fading is a prominent problem that affects the quality of mobile communication. Usually, technologies such as space diversity and adaptive equalization must be used to overcome it, and there is a large fading margin. CDMA systems can use multipath signals to provide path diversity, which not only alleviates Rayleigh fading, but also slows down slow fading caused by physical occlusion, thereby greatly improving communication quality.
3. Increased system capacity For FDMA and TDMA, once the frequency point or time slot of the cell is allocated, the cell cannot receive new calls, and the capacity has a hard limit. However, CDMA is an interference-limited system. Under the specified interference level, even when the number of users has reached a limited number, it is also allowed to add individual users. The disadvantage is that the voice quality is degraded. Service providers can balance capacity and voice quality. CDMA's precise power control and soft handoff techniques greatly reduce the strength of the interfering signal and the required signal-to-noise ratio requirements, and effectively employ techniques such as voice activation or variable rate voice coding, diversity reception, and power control. According to reports, the signal-to-noise ratio of CDMA is 3.7 times that of DAMPS and TDMA, 11.2 times that of TACS, 13.6 times that of AMPS, and 20 times that of FM/FDMA.
4. The communication quality is good. The CDMA system adopts the direct sequence spread spectrum technology, and comprehensively applies various diversity technologies such as time diversity, frequency diversity, space diversity, and path diversity to overcome the multipath effect, and can obtain strong anti-interference ability. During handover, the soft handover technology of first establishment and then interruption is adopted, which ensures the communication quality of CDMA, especially when there is no ping-pong effect during handover. The system is broadband and low-noise ratio, and the waveform allows the use of high-redundancy error-correcting coding and efficient digital modulation techniques to ensure high-quality voice and data transmission.
5. High frequency utilization The same frequency of the CDMA system can be reused in all cells, and its frequency reuse rate is 2/3 (the frequency reuse rate of FDMA and TDMA is 1/7). configuration, which greatly simplifies cell splitting and microcell introduction.
6. Strong multiple access capability The multiple access capability of the CDMA system determines the multiple access interference between spread spectrum codes, which is related to the spread spectrum coding scheme used, and the multiple access interference between users who transmit signals at the same time (ie, the related characteristics of spread spectrum codes) It is related to the allowable reception quality (output signal-to-noise ratio), so the lower the multiple access interference between simultaneous working users, the lower the allowable reception quality, and the stronger the multiple access capability of CDMA technology.
7. Highly reliable secrecy security CDMA mobile communication system is a secure communication system. If a certain encryption algorithm technology is added, the communication security performance can be greatly improved, which is unmatched by FDMA and TDMA systems. Analyzing the spread spectrum system it adopts, it is almost impossible to intercept other people's communication content. For example, as long as the lithium battery in the machine is not discharged, it changes the real-time state of its sequence at a clock frequency of 512KHz, even if it is working continuously. , its spread spectrum address sequence period is also up to 7 years. It can also easily set and change the master key, secondary key, spread spectrum code table, standard encryption algorithm, etc. in the CDMA system, so that the confidentiality of communication is more reliable.
8. Small mobile phone power consumption After CDMA adopts power control, the transmit power level is only increased during the fading period, thereby reducing the average transmit power. The minimum power of FDMA is 5mW, the average transmit power is 794mW, and the peak power is 3W, while CDMA The minimum power is 2.3mW, the average transmit power is 5mW, and the peak power is 100mW. It can be seen that the average transmit power and maximum transmit power of CDMA are lower than those of FDMA, thereby increasing the system capacity, reducing the number of cells and reducing equipment costs.