Rx Sensitivity

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1. Rx Sensitivity (Receiver Sensitivity) Receiver sensitivity is one of the most basic concepts in the field of communications. It is used to describe the minimum signal strength that a receiver can identify without exceeding a certain bit error rate. The bit error rate usually refers to the bit error rate (BER) or the packet error rate (PER). This definition comes from the circuit switching era, while in the LTE era, throughput is more likely to be used to measure sensitivity. Since LTE no longer has circuit-switched voice channels, throughput has become a more practical measure. This is also an evolution of communication technology, because now we no longer use "standardized substitutes" such as 12.2kbps RMC (reference measurement channel, which actually represents a voice coding rate of 12.2kbps) to measure sensitivity, but define it based on the throughput actually felt by the user.

Receiver sensitivity is critical to the performance of wireless communication systems. If the receiver sensitivity is low, then signals with weak signal strength cannot be correctly received and decoded, resulting in communication failure or reduced communication quality. Therefore, improving receiver sensitivity is one of the important means to improve the performance of wireless communication systems.

In practical applications, the value of receiving sensitivity is affected by many factors. The first is the performance of the antenna system. The gain and directivity of the antenna will affect the received signal strength. The second is the signal transmission environment, including distance, obstacles, multipath effects, etc. In addition, the hardware design and decoding algorithm of the receiver will also affect the value of receiving sensitivity.

In the design of wireless communication systems, it is usually necessary to maximize the receiving sensitivity while ensuring a certain bit error rate. This can be achieved by optimizing the antenna system, selecting appropriate modulation and coding methods, and optimizing the receiver hardware design and decoding algorithm.

In short, receiving sensitivity is one of the most important concepts in wireless communication systems and plays an important role in improving the performance of communication systems.

2. SNR (Signal-to-Noise Ratio)
When discussing receiver sensitivity, the signal-to-noise ratio (SNR) is often mentioned, especially the demodulation signal-to-noise ratio of the receiver. The demodulation signal-to-noise ratio refers to the signal-to-noise ratio threshold that the demodulator can demodulate without exceeding a certain bit error rate. So what do S and N stand for?
S stands for signal, also known as useful signal, which is generally emitted by the transmitter of the communication system. And N stands for noise, which refers to all signals without useful information. The sources of noise are very wide, the most typical of which is the famous -174dBm/Hz, the natural noise floor. It should be noted that this quantity is independent of the type of communication system and is derived from thermodynamics, so it is related to temperature. In addition, it is actually the noise power density, so we receive the same bandwidth of noise as the signal with the same bandwidth. Therefore, the final noise power is obtained by integrating the noise power density over the bandwidth.

Transmit power is very important in communication systems because the signal needs to go through spatial fading to reach the receiver, and high transmit power means a longer communication distance. So is the SNR of the transmitted signal important? If the SNR of the transmitted signal is poor, will the SNR of the signal received by the receiver also be poor?
3. This involves the concept of natural noise floor. We assume that spatial fading has the same effect on signal and noise (although this is not actually the case, signals can be coded to resist fading, but noise cannot), and acts like an attenuator. Assuming the spatial fading is -200dB, the bandwidth of the transmitted signal is 1Hz, the power is 50dBm, and the signal-to-noise ratio is 50dB, what is the SNR of the signal received by the receiver? The
signal power received by the receiver is 50-200=-150dBm (bandwidth 1Hz), while the noise power of the transmitter is 50-50=0dBm, and the power reaching the receiver through spatial fading is 0-200=-200dBm (bandwidth 1Hz)? At this point, this part of the noise has been "submerged" under the natural noise of -174dBm/Hz. Therefore, when calculating the noise at the receiver entrance, only the "basic component" of -174dBm/Hz needs to be considered.
In most cases of communication systems, this assumption is applicable.

4. ACLR/ACPR refers to the adjacent channel leakage ratio and adjacent channel leakage power ratio, which are used to describe the interference caused by the transmitter leaking into the adjacent channel. These interferences are not in the transmission channel, but affect other devices. ACLR and ACPR are both named after "adjacent channels" and are used to describe the interference caused by the transmitter to other devices. What they have in common is that the power calculation of the interference signal is based on a channel bandwidth. This measurement method shows that the design purpose of this indicator is to consider the interference caused by the signal leaked by the transmitter to the receiver of the same or similar equipment. In LTE, there are two settings for ACLR testing, EUTRA and UTRA. The former describes the interference of LTE system to LTE system, and the latter considers the interference of LTE system to UMTS system. Therefore, ACLR/ACPR describes a kind of "peer" interference: the interference caused by the leakage of the transmitted signal to the same or similar communication system. This definition is very important in the actual network, because the same cell, adjacent cells and nearby cells often have signal leakage, so the process of network planning and optimization is actually the process of maximizing capacity and minimizing interference, and the adjacent channel leakage of the system itself is a typical interference signal for the adjacent cells. In the evolution of communication systems, the goal has always been "smooth transition", that is, upgrading and transforming the existing network into the next generation network. Therefore, the coexistence of two or even three generations of systems requires consideration of the interference between different systems. The introduction of UTRA in LTE takes into account the radio frequency interference of LTE to the previous generation system when it coexists with UMTS.

5. In the GSM system, Modulation Spectrum and Switching Spectrum play a similar role to adjacent channel leakage. The difference is that their measurement bandwidth is not the occupied bandwidth of the GSM signal. Modulation spectrum is used to measure the interference between synchronous systems, while switching spectrum is used to measure the interference between asynchronous systems. If the signal is not gated, the switching spectrum will overwhelm the modulation spectrum.
In the GSM system, the cells are not synchronized, although TDMA technology is used. In contrast, TD-SCDMA and later TD-LTE cells are synchronized. Due to the lack of synchronization between cells, the power leakage of the rising/falling edge of cell A may fall on the payload part of cell B. Therefore, we use the switching spectrum to measure the interference of the transmitter to the adjacent channel in this state; while in the entire 577us GSM timeslot, the proportion of the rising/falling edge is small, and most of the time the payload parts of two adjacent cells will overlap in time. The modulation spectrum can be used to evaluate the interference of the transmitter to the adjacent channel in this case.

6. SEM (spectrum emission mask) is an "in-band indicator" used to measure the in-band spectrum leakage of the transmitter. Unlike spurious emissions, SEM mainly provides a "spectrum template" to detect whether the in-band spectrum exceeds the limit. It is related to ACLR, but different: ACLR considers the average power leaked into the adjacent channel, and uses the channel bandwidth as the measurement bandwidth. It reflects the "noise floor" of the transmitter in the adjacent channel; SEM reflects the excessive points captured in the adjacent frequency band with a smaller measurement bandwidth, reflecting the "spurious emission based on the noise floor". If you scan the SEM with a spectrum analyzer, you can see that the spurious points on the adjacent channel are generally higher than the ACLR average. If the ACLR indicator itself has no margin, SEM will easily exceed the standard. However, SEM exceeding the standard does not necessarily mean that ACLR is poor. It may be caused by LO spurious or a clock and LO modulation component in series with the transmitter link. The use of SEM can help evaluate the in-band spectrum leakage of the transmitter.

tagetage

Good basic concept, thumbs up.