Hello,
introduction
As mobile communications move towards the LTE era, greater backhaul bandwidth is required. According to forecasts, the service throughput of a single base station will reach more than 1Gbit/s.
Microwave links are one of the main methods for base station business backhaul, and providing larger and more efficient air interface bandwidth is the main goal of microwave communication technology development.
How to provide greater air interface bandwidth?
There are two main methods:
one is to improve the transmission efficiency of microwave communication on the existing spectrum resources;
the other is to expand more spectrum resources.
So the question is, in the ultra-wideband era, which microwave air interface bandwidth mining technology is strong?
Ultra-high modulation mode-improve spectrum utilization
Quadrature amplitude modulation (Quadrature Amplitude Modulation, QAM) is a commonly used modulation method in modern communication systems. In the QAM modulated signal actually used, each symbol represents an N-bit binary number, which may represent M states (M=2N). The QAM modulation mode with M states is also called MQAM mode. Common QAM modulation modes include 4QAM, 16QAM, 32QAM, 64QAM, 128QAM, 256QAM, etc.
Note:
1. For unmodulated binary baseband signals, each symbol (symbol) represents a binary number, and its symbol set has two states: "0" and "1".
2. The modulation effects of 4QAM and QPSK are equivalent, but QSPK only needs one carrier, which is simpler to implement, so the actual equipment usually uses QPSK instead of 4QAM.
QAM is realized by amplitude modulation of two orthogonal signals, which can be visually represented on a plan view, called a constellation diagram. Each constellation point on the constellation diagram corresponds to a signal in the transmission signal set. From the figure, we can see intuitively that the more constellation points, the greater the amount of information that each symbol can transmit.
In the transmission process, the interference of noise appears to make the signal deviate from the accurate position of its corresponding constellation point. When the average energy of the constellation diagram remains unchanged, adding constellation points will reduce the distance between the constellation points, which requires a higher signal-to-noise ratio to correctly analyze the signal.
If each symbol is regarded as a trolley carrying goods, the higher the modulation mode, the more goods the trolley can carry.
It can be seen that under the same symbol rate, the higher the modulation mode, the larger the service capacity. In theory, the service capacity of the 2N+1QAM modulation mode is (N+1)/N times that of the 2NQAM mode.
At the same time, cars with more cargo also place higher demands on road conditions. That is, it is required that the transmission channel is stable and has low interference, and there is an excellent demodulation technology to demodulate the received signal.
Note:
Under actual engineering conditions, due to multipath fading and other reasons, the quality of the transmission channel is changeable, so the ultra-high modulation mode is usually used with AM (Adaptive Modulation) technology.
Huawei's RTN300 and RTN900 series of IP microwave products fully support 1024QAM/2048QAM ultra-high modulation mode, and are the first to support 4096QAM ultra-high modulation mode, with a spectrum efficiency of up to 9.6bps/Hz, which can make full use of spectrum resources.
On the channel bandwidth of 56MHz, RTN microwave can adopt 4096QAM modulation mode to achieve a service capacity of 500+Mbit/s, which is 45% higher than the traditional IP microwave 256QAM.
That's all for today, you are welcome to leave a message and exchange in the comment area. Thank you!
