Introduction Radio Frequency Identification (RFID) is a type of automatic identification technology that uses radio frequency to carry out wireless non-contact two-way data communication, with recording media (electronic tags or radio frequency cards) to read and write. The purpose is identifying the target and making data exchange. This is an extremely complex system, so it involves many parameters. Next, we will introduce several important parameters in detail. What is RFID? How RFID works? Catalog Introduction Ⅰ RFID Parameters Explained 1.1 Rx Sensitivity 1.2 SNR (Signal-to-Noise Ratio) 1.3 Tx Power 1.4 ACLR/ACPR 1.5 Modulation Spectrum/Switching Spectrum 1.6 SEM (Spectrum Emission Mask) 1.7 EVM (Error Vector Magnitude) 1.8 Interference Indicators 1.9 Dynamic Range, Temperature Compensation and Power Control Ⅱ FAQ Ⅰ RFID Parameters Explained Radio frequency identification involves many settings, that is, parameter selections. What are they? Here gives you the detailed descriptions as following mentioned. 1.1 Rx Sensitivity Receiving sensitivity is one of the most basic concepts, characterizes the lowest signal strength that the receiver can recognize without exceeding a certain bit error rate (BER), which is a general term that follows the definition of the circuit switched (CS) era. In most cases, BER or Packet Error Rate (PER) will be used to examine the sensitivity. In the Long Term Evolution (LTE) era, use throughput to define simply. LTE does not have a circuit-switched voice channel, but this is also a real evolution. Because for the first time we no longer use "standardization" such as 12.2kbps RMC (voice coding at 12.2kbps) to measure sensitivity, but the throughput that users can really feel. 1.2 SNR (Signal-to-Noise Ratio) When talking about sensitivity, we often refer to SNR (signal-to-noise ratio), we generally talk about the demodulation SNR of the receiver. We define it as the ability of the demodulator to not exceed a certain bit error rate, that is, SNR threshold for demodulation.So where do S and N come from? S means Signal, or useful signal; N means Noise. The useful signal is generally emitted by the communication system transmitter, and the source of noise is very wide. The most typical one is the famous -174dBm/Hz (natural noise). It is a quantity that has nothing to do with the type of communication system. In a sense, it is actually a noise power density related to temperature. In addition, how much bandwidth do we receive determine the noise, that is, the final noise power is integrated on the bandwidth by the noise power density. 1.3 Tx Power The importance of the transmission power is that the signal from the transmitter needs to pass through the fading of space to reach the receiver. So the higher the transmission power means the longer the communication distance.So should we consider SNR for our transmitted signal? For example, if the SNR of our transmitted signal is very poor, do we receive the same bad?This involves the concept just mentioned, the natural noise we assume that spatial fading has the same effect on both signal and noise (in fact, it is not, the signal can resist fading through coding but noise not) and it acts like an attenuator. For example, we assume spatial fading is -200dB, the transmitted signal bandwidth is 1Hz, the power is 50dBm, and the SNR is 50dB, then what is the SNR received by the receiver?The power of the signal received by the receiver is 50-200=-150Bm (bandwidth 1Hz), and the noise of the transmitter 50-50=0dBm through spatial fading, and the power reaching the receiver is 0-200=-200dBm (bandwidth 1Hz)? At this time, this part of the noise has already been "submerged" under the natural noise -174dBm/Hz. At this time, we only need to consider the "basic component" of -174dBm/Hz to calculate the noise to the receiver. Actually, this is applicable in most cases of communication systems. 1.4 ACLR/ACPR These parameters are explained together because they actually represent part of the "transmitter noise", but these noises are not in the transmitting channel, but the part that the transmitter leaks into the adjacent channels, which can be collectively referred to as "Leakage in the adjacent channel".ACLR and ACPR (actually one thing, but one is called in the terminal test, the other is called in the base station test), both are named after "Adjacent Channel". They both describe the machine pair interference from other equipment. And their power calculation of the interference signal is also based on a channel bandwidth. This measurement method considers the signal leaked by the transmitter and the interference to the equipment receiver of the same or similar standard-the interference signal falls into the receiver band with the same frequency and the same bandwidth. That is, form the same frequency interference to the signal received by the receiver.In LTE, the ACLR test has two settings: EUTRA and UTRA. The former describes the interference among the LTE systems, and the latter considers the interference of the LTE system to the UMTS system. So we can see that the measurement bandwidth of EUTRAACLR is the occupied bandwidth of LTE RB, and the measurement bandwidth of UTRA ACLR is the occupied bandwidth of UMTS signals (FDD system 3.84MHz, TDD system 1.28MHz). In other words, ACLR/ACPR describes a kind of "peer-to-peer" interference: the leakage of the transmitted signal interferes with the same or similar communication system.This definition is significant. For example, in the actual network, there are often signal leakage from neighboring cells from other or in the same region. In other words, the adjacent channel leakage of the system itself is typical for neighboring cells. Therefore, the process of network planning and optimization is actually the process of capacity maximization and interference minimization. In addition, from the other side of the system, the mobile phones of users in crowded people may also become a source of mutual interference.Similarly, in the evolution of communication systems, the goal has always been to "smooth transition", that is, to upgrade and transform existing networks into next-generation networks. Therefore, the coexistence of two or even three generations of systems should consider the interference between different systems. So the introduction of UTRA in LTE is to consider the radio frequency interference to the previous generation system UMTS. 1.5 Modulation Spectrum/Switching Spectrum In the GSM system, Modulation Spectrum and Switching Spectrum also play a similar role to adjacent channel leakage. The difference is that their measurement bandwidth is not the occupied bandwidth of the GSM signal. From a definition point of view, it can be considered that the modulation spectrum is a measure of the interference between synchronous systems, and the switching spectrum is a measure of the interference between asynchronous systems. In fact, if the signal is not gating, the switching spectrum will definitely cover the modulation spectrum.This involves another concept: in the GSM system, the cells are not synchronized, although it uses TDMA. In contrast, TD-SCDMA and later TD-LTE, the cells are synchronized.Because the cells are not synchronized, the power leakage of the rising edge/falling edge of the A cell may fall to the payload part of the B cell, so we use the handover spectrum to measure the interference of the transmitter to the adjacent channel in this state. And in the entire 577us GSM timeslot, the proportion of rising edge/falling edge is very small after all. What’s more, most of the time, the payload of two adjacent cells will overlap in time. In this case, the interference of the transmitter to the adjacent channel can be evaluated by referring to the modulation spectrum. Figure 1. RFID Chip 1.6 SEM (Spectrum Emission Mask) SEM is an in-band indicator, which is distinguished from spurious emission. The latter includes SEM, but the focus is on the spectrum leakage outside the working frequency band of the transmitter. In addition, its introduction is more based on the perspective of EMC (Electromagnetic Compatibility).SEM provides a spectrum template. When measuring the spectrum leakage in the transmitter band, see if there are any points that exceed the template limit. It can be said that it is related to ACLR, but it is not the same. ACLR considers the average power leaked into the adjacent channel, so it uses the channel bandwidth as the measurement bandwidth, and it reflects the "critical noise point" of the transmitter in the adjacent channel. Where SEM reflects the capture of over-standard points in adjacent frequency bands with a smaller measurement bandwidth (usually 100kHz to 1MHz), which reflects the noise-based spurious emission.If you scan the SEM with a spectrum analyzer, you can see that the spurious points on the adjacent channel will generally be larger than the ACLR average. Therefore, if the ACLR indicator itself has no margin, the SEM will easily exceed it. On the other hand, if the SEM exceeds the ACLR, it does not necessarily mean bad. For example, a common phenomenon is that there is LO spurious or a certain clock and LO modulation component (often very narrow bandwidth, similar to dot frequency) in the transmitter link, although ACLR is good, the SEM may exceed the standard. 1.7 EVM (Error Vector Magnitude) EVM is a vector, which means it has amplitude and angle. It measures the error between the actual signal and the ideal signal. This measurement can effectively express the "quality" of the transmitted signal. That is, the farther the point distance of the actual signal to the ideal signal, the greater the error and the greater the modulus of the EVM.Why is the SNR of the transmitted signal not so important? There are two reasons: the first is that it is often much higher than the SNR required for demodulation of the receiver. The second is the condition, that is, the worst case. The transmitter noise has already been submerged under the natural noise after a large spatial fading, and the useful signal is also attenuated to near the demodulation threshold of the receiver.But the "intrinsic SNR" of the transmitter needs to be considered in some cases, such as short-range wireless communication. Even without considering the spatial fading, demodulation of such high-order quadrature modulated signals alone already requires a high SNR. The worse the EVM, the worse the SNR and the higher the difficulty of demodulation. Engineers working on 802.11 systems often use EVM to measure Tx linearity. While engineers working on 3GPP systems, they like to use ACLR/ACPR/Spectrum to measure it.From the origin, 3GPP is the evolutionary path of cellular communication, and from the very beginning it has to pay attention to adjacent channel and alternative channel interference. In other words, interference is the number one obstacle that affects cellular communication rates. Therefore, 3GPP always aims at "minimizing interference" during its evolution, such as frequency hopping in the GSM era, spread spectrum in the UMTS era, and the RB concept in LTE era.The 802.11 system is an evolution of fixed wireless access. It follows the spirit of the TCP/IP protocol and aims at "service first". In 802.11, there use often time division or frequency hopping methods to achieve multi-user coexistence. The network layout is more flexible, and the channel width is also flexible and variable. In general, it is not sensitive to interference (or rather high tolerance).In layman's terms, the origin of cellular communication is to make phone calls, and users who cannot get through the phone will go to the telecommunications; while the origin of 802.11 is the local area network, you just wait at first when the network is not good.So this determines that the 3GPP series must take ACLR/ACPR and other "spectrum regeneration" performance as indicators, while the 802.11 series can adapt to the network environment at the expense of speed.Specifically, "Adapt to the network environment at the expense of speed" means that in the 802.11 series, different modulation orders are used to cope with the propagation conditions. When the receiver finds a signal difference, it immediately informs the opposite transmitter to reduce the modulation order. As mentioned earlier, SNR and EVM in an 802.11 system are highly correlated. To a large extent, a reduction in EVM can improve SNR. In this way, we have two ways to improve the receiving performance: one is to reduce the modulation order, thereby reducing the demodulation threshold; the other is to reduce the transmitter EVM, so that the signal SNR is improved.Because EVM is closely related to the demodulation effect of the receiver, EVM is used to measure the performance of the transmitter in the 802.11 system (similarly, in 3GPP, ACPR/ACLR is the index that mainly affects the network performance). In addition, the deterioration of EVM is mainly caused by non-linearity (for example, AM-AM distortion of PA), so EVM is usually used as a sign to measure the linear performance of the transmitter. Figure 2. RFID 1.7.1 Relations of EVM to ACPR / ACLR It is difficult to define the quantitative relationship between EVM and ACPR/ACLR. From the non-linearity of the amplifier, EVM and ACPR/ACLR should be positively correlated. That is, the AM-AM and AM-PM distortion of the amplifier will amplify the EVM, and also the ACPR/ACLR.However, EVM and ACPR/ACLR are not always positively correlated. For example, Clipping is commonly used in digital IF. It is to reduce the peak-to-average ratio (PAR) of the transmitted signal. The reduction of peak power can help reduce the ACPR/ACLR after passing through the PA. However, clipping will also damage the EVM. Because whether it is clipping (windowing) or using a filter, they all cause damage to the signal waveform, affecting the EVM. 1.7.2 Source Flow of PAR PAR (Peak-to-Average Ratio) is usually represented by a statistical function such as CCDF, and its curve represents the power (amplitude) value of the signal and its corresponding probability of occurrence. For example, if the average power of a certain signal is 10dBm, the statistical probability that it has a power exceeding 15dBm is 0.01%, and we can consider its PAR is 5dB.PAR is an important factor affecting transmitter spectrum regeneration (such as ACLP/ACPR/Modulation Spectrum) in modern communication systems. The peak power will push the amplifier into the nonlinear region and produce distortion. And the higher the peak power, the stronger the nonlinearity.In the GSM era, because of the constant envelope characteristic of GMSK modulation, PAR is 0. When designing GSM power amplifiers, we often push it to P1dB to get the maximum efficiency. After the introduction of EDGE, 8PSK modulation is no longer a constant envelope, so we tend to push the average output power of the amplifier to about 3dB below P1dB, because the PAR of the 8PSK signal is 3.21dB.In the UMTS era, whether WCDMA or CDMA, the PAR is much larger than that of EDGE. The reason is the correlation of the signals in the code division multiple access system. In other words, when the signals of multiple code channels are superimposed in the time domain, the same phase may occur, and the power will show a peak at this time.The PNR of LTE is derived from the burstiness of the RB. OFDM modulation is based on the principle of dividing multi-user/multi-service data into blocks in both the time domain and the frequency domain, so that high power may appear in a certain "time block". LTE uplink transmission uses SC-FDMA. First, DFT extends the time domain signal to the frequency domain, which is equivalent to "smoothing" the burstiness in the time domain, thereby reducing PAR. Figure 3. RFID Applications 1.8 Interference Indicators The "interference index" here refers to the sensitivity test under various applied interferences in addition to the static sensitivity of the receiver. In fact, it is very interesting to study the origin of these test items.Our common interference indicators include Blocking, Desense, Channel Selectivity, etc. 1.8.1 Blocking Blocking is actually a very old RF indicator, as early as the invention of radar. The principle is to pour a large signal into the receiver (usually the first LNA that suffers the most), making the amplifier enter the nonlinear region or even saturate. At this time, on the one hand, the amplifier gain suddenly becomes smaller, and on the other hand, extremely strong nonlinearity occurs, so the function of amplifying useful signals cannot work normally.Another possible Blocking is actually done through the receiver's AGC. Large signals enter the receiver link, and the receiver AGC will reduce the gain to ensure dynamic range, but the useful signal level entering the receiver is very low. At this time, the gain is insufficient, and the amplitude of the useful signal entering the demodulator is insufficient.Blocking indicators are divided into in-band and out-of-band, mainly because the RF front-end generally has a band filter, which has an inhibitory effect on out-of-band blocking. However, the blocking signal is generally point frequency without modulation. In fact, point-frequency signals without modulation at all are rare in practice. In engineering, it is approximately point-frequency to replace various narrow-band interference signals.For solving Blocking, the key is RF. In other words, it is to expand the dynamic range of receiver. For out-of-band blocking, the rejection of the filter is also very important. 1.8.2 AM Suppression AM Suppression is a unique indicator of the GSM system. From the description point of view, the interference signal is a TDMA signal similar to the GSM signal, synchronized with the useful signal and has delay.This scenario simulates the signal of the neighboring cell in the GSM system. From the point of view that the frequency offset of the interference signal is greater than 6MHz (GSM bandwidth is 200kHz), this is a very typical neighboring cell signal configuration. So we can think that AM suppression is a reflection of the receiver's interference tolerance to neighboring cells in the actual work of the GSM system.Adjacent (Alternative) Channel Suppression (Selectivity)Here we collectively refer to it as "adjacent channel suppression". In the cellular system, in addition to the same-frequency cells, we must also consider adjacent-frequency cells in our networking. The reason can be found in the transmitter index ACLR/ACPR/Modulation Spectrum that we discussed before. Because of the transmitter's spectrum regeneration, there will be strong signals falling into adjacent frequencies (generally, the farther the frequency offset, the lower the level, so the adjacent channel is generally the most affected), and this kind of spectrum regeneration is actually related to the transmitted signal. That is, receivers of the same standard are likely to mistake this part of the regenerated spectrum as a useful signal for demodulation.For example, if two neighboring cells A and B happen to be neighboring frequency cells (such networking methods are generally avoided, here is just a assumption), when a terminal registered in cell A swims to the campus junction of two, but the signal strength of the two cells has not reached the handover threshold, the terminal still maintains cell connection with A, and the ACPR of the B cell base station transmitter is higher. So the terminal’s receiving frequency band has a higher ACPR component of B cell, which overlaps with the useful signal of cell A in frequency. Because the terminal is far away from the base station of cell A at this time, the received signal is weak. At this time, when the ACPR component of cell B enters the terminal receiver, it causes co-channel interference to the original useful signal.If we pay attention to the definition of the frequency offset of the adjacent channel selectivity, we will find that there is a difference between Adjacent and Alternative, which corresponds to the first and second adjacent channels of ACLR/ACPR. It can be seen that the "transmitter spectrum leakage (regeneration)" in the communication protocol and the "receiver adjacent channel selectivity" are actually defined in pairs. 1.8.3 Co-Channel Suppression (Selectivity) Co-frequency interference generally refers to the interference pattern between two cells.According to the networking principles we described earlier, the distance between two cells with the same frequency should be as far as possible. In addition, even if they are farther away, there will be signals leaking to each other, but the difference is in intensity. For the terminal, the signals of the two campuses can be regarded as "correct and useful signals" (of course, there is a set of access specifications on the protocol layer to prevent such false access). Frequency strength of both depends on its co-frequency selectivity. 1.8.4 Summery Blocking is big signal interferes with small signal, but the AM Suppression is small signal interferes with large signal.Single-tone Desense is a unique indicator of the CDMA system. It has a feature: the single-tone is an in-band signal and is very close to the useful signal. In this way, it is possible to generate two kinds of signals falling into the receiving frequency domain: First is due to near-end phase noise of the LO, the baseband signal formed by the mixing of the LO and the useful signal, and the signal formed by the mixing of the LO phase noise and the interference signal. Both will fall within the range of the receiver baseband filter, the former is a useful signal and the latter is interference. Second is due to the nonlinearity in the receiver system. The useful signal (with a certain bandwidth, such as 1.2288MHz CDMA signal) may produce intermodulation with the interference signal on the nonlinear device, falling in the receiving frequency domain and becoming interference.The origin of single-tone desense is that the CDMA system uses the same frequency band as the original analog communication system AMPS, and the two networks coexisted for a long time. So the CDMA system must consider the AMPS system's interference to itself.The explanation of Blocking in theory: the large signal entering the receiver causes the amplifier to enter the nonlinear region, and the actual gain becomes smaller (for useful signals).But it is difficult to explain two scenarios:Scenario 1: The pre-stage LNA has a linear gain of 18dB. When a large signal is injected to make it reach P1dB, the gain is 17dB. If no other influence is introduced (the default LNA NF, etc. have not changed), then the noise figure of the entire system is actually very limited. It is nothing more than the fact that the denominator of the latter-stage NF becomes a little smaller when it is included in the total NF, which has little effect on the sensitivity of the entire system.Scenario 2: The IIP3 of the previous LNA is very high, so it is not affected. The second level gain block is affected (the interference signal makes it reach near P1dB). In this case, the impact of the entire system NF is even smaller.Here is a point of view: the influence of Blocking may be divided into two parts. One part is that the gain mentioned in the textbook is compressed, and the other part is actually that after the amplifier enters the nonlinear region, the useful signal is distorted in this region. This kind of distortion may include two parts, one part is the spectrum regeneration (harmonic component) of the useful signal caused by pure amplifier nonlinearity, and the other part is the Cross Modulation of the large signal modulating the small signal.From this we also put forward another idea: if we want to simplify the Blocking test (3GPP requires frequency sweeping, which is very time-consuming), we may be able to select certain frequency points, which have the greatest impact on useful signal distortion when the Blocking signal appears.From an intuitive point of view, these frequency points may have: f0/N and f0*N (f0 is the useful signal frequency, and N is a natural number). The former is because the N-th harmonic component generated by the large signal in the nonlinear region is just superimposed on the useful signal frequency f0 to form direct interference, and the latter is superimposed on the N-th harmonic of the useful signal f0 and affects the output signal f0.According to Pascal's law, the waveform of the time domain signal is actually the sum of the domain fundamental frequency signal and each harmonic. When the power of the Nth harmonic in the frequency domain changes, the corresponding in the domain is the envelope change of the time domain signal (have distortion). Figure 4. RFID Readers 1.9 Dynamic Range, Temperature Compensation and Power Control These three indicators will only be shown when certain extreme tests are performed, but they themselves represent the most significant part of RF design. 1.9.1 Dynamic Range of the Transmitter The dynamic range of the transmitter characterizes the maximum and minimum transmission power without damaging other transmission indicators. This concept is very broad. If you look at the main effects, you can understand that the linearity of the transmitter is not compromised at the maximum transmission power, and the SNR of output signal is maintained at the minimum transmission power.Under the maximum transmit power, the output is often close to the nonlinear region of active devices at all levels (especially the final amplifier), and the nonlinearity that often occurs is spectral leakage and regeneration (ACLR/ACPR/SEM), modulation error (PhaseError/EVM). The most susceptible at this time is basically the linearity of the transmitter.Under the minimum transmit power, the useful signal output by the transmitter is close to the natural noise of the transmitter, and may even be submerged in the transmitter noise. At this time, what needs to be guaranteed is the SNR of the output signal. In other words, the lower the transmitter noise at the minimum transmit power, the better. 1.9.2 Dynamic Range of the Receiver The dynamic range of the receiver is actually related to the two indicators we talked about before, the first is the reference sensitivity, and the second is the receiver IIP3 (interference indicator).The reference sensitivity actually characterizes the minimum signal strength that the receiver can recognize. We mainly talk about the maximum receiving level of the receiver.It refers to the maximum signal that the receiver can receive without distortion. This distortion may occur at any stage of the receiver, from the previous LNA to the receiver ADC. For the front-level LNA, the only thing we can do is to increase IIP3 as much as possible so that it can withstand higher input power. For the subsequent step-by-step devices, the receiver uses AGC (automatic gain control) to ensure that the useful signal falls on the device within the input dynamic range. Simply put, there is a negative feedback loop: detect the received signal strength (too low/too high)-adjust the amplifier gain (up/down)-the amplifier output signal to ensure that it falls within the input dynamic range of the next stage device.Here we talk about an exception: the front-end LNA of most mobile phone receivers has AGC function. If you study their datasheet carefully, you will find that the front-end LNA provides several variable gain sections, and each gain section has its corresponding noise factor. Generally speaking, the higher the gain, the lower the noise factor. This is a simplified design. The design goal of the receiver RF link is to keep the useful signal input to the receiver ADC within the dynamic range and keep the SNR higher than the demodulation threshold (the SNR is not critical, but "just enough"). Therefore, when the input signal is large, the front-stage LNA reduces gain, loss NF, and increases IIP3 at the same time. When the input signal is small, the front-stage LNA increases gain, reduces NF, and meanwhile reduces IIP3. Figure 5. RFID Discover 1.9.3 Temperature Compensation Generally speaking, we only have temperature compensation in the transmitter. Of course, the receiver performance is also affected by temperature. On the one hand, the receiver link gain decreases at high temperatures, and NF increases. On the other hand, at low temperatures, receiver link gain increases, and NF decreases. However, due to the small signal characteristics of the receiver, both gain and NF are within the range of system redundancy.It can also be subdivided into two parts: one part is the compensation for the power accuracy of the transmitted signal, and the other part is the compensation for the change in the transmitter gain with temperature.Transmitters of modern communication systems generally perform closed-loop power control (except for the slightly "old" GSM system and Bluetooth system). Therefore, the power accuracy of transmitters calibrated through production procedures actually depends on the accuracy of the power control loop. Generally speaking, the power control loop is a small signal loop, and the temperature stability is very high, so the demand for temperature compensation is not high, unless there are temperature-sensitive devices (such as amplifiers) on the power control loop.Temperature compensation for transmitter gain is more common, which has two common purposes:One is "visible", usually for systems without closed-loop power control (such as the aforementioned GSM and Bluetooth), this type of system usually does not require high output power accuracy, so the system can apply a temperature compensation curve (function) to keep the RF link gain within an interval. So that when the baseband IQ power is fixed and the temperature changes, the RF power output by the system can also be kept within a certain range.The other is "invisible", usually in a system with closed-loop power control. Although the RF output power of the antenna port is precisely controlled by the closed-loop power control, we need to keep the DAC output signal within a certain range (A common example is the need for digital predistortion (DPD) of the base station transmission system), then we need to control the gain of the entire RF link more accurately around a certain value.In the early stage of low accuracy and low cost accuracy requirements, temperature compensation attenuators are more common. Require higher accuracy requirements, the solution generally: temperature sensor + digital attenuator/amplifier + production calibration. 1.9.4 Power Control of the Receiver After talking about dynamic range and temperature compensation, let's talk about a related and very important index: power control.Transmitter power control is a necessary function in most communication systems. Commonly used in 3GPP, such as ILPC, OLPC, and CLPC. In addition, it must be tested in RF design.All transmitter power control purposes include two points: power consumption control and interference suppression.Let’s first talk about power consumption control: In mobile communications, in view of the changes in the distance between the two ends and the different levels of interference, for the transmitter, it is only necessary to maintain the signal strength enough for the receiver of the other party to demodulate accurately. If it is low, the communication quality is impaired, and if it is too high, the empty power consumption is meaningless. This is especially true for battery-powered terminals like mobile phones.Interference suppression is a more advanced requirement. In CDMA-type systems, because different users share the same carrier frequency (differentiated by orthogonal user codes), in the signal arriving at the receiver, user's signal is covered by the same frequency for other users. If the signal power of each user is high or low, the high-power user will drown out the low-power user’s signal. Therefore, the CDMA system adopts a power control method to control the power of different users reaching the receiver, and sends a power control command to each terminal to make the air interface power of each user the same. This kind of power control has two characteristics: the first is that the power control accuracy is very high (the interference tolerance is very low), and the second is that the power control cycle is very short (the channel may change quickly).In the LTE system, uplink power control also has the effect of interference suppression. Because LTE uplink is SC-FDMA, and multiple users also share carrier frequencies, which also interfere with each other, so the same air interface power.The GSM system also has power control. In GSM, we use power level to characterize the power control step length, each level is 1dB. It can be seen that GSM power control is relatively rough.Interference Limited SystemHere is a related concept: interference limited system. The CDMA system is a typical interference limited system. In theory, if each user code is completely orthogonal and can be completely distinguished by interleaving and de-interleaving, then the capacity of the CDMA system can be infinite. Because it can be used on limited frequency resources. The user code extended layer by layer distinguishes an infinite number of users. But in fact, since the user codes cannot be completely orthogonal, noise is inevitably introduced during multi-user signal demodulation. The more users there are, the higher the noise will be, until the noise exceeds the demodulation threshold. In other words, the capacity of the CDMA system is limited by interference (noise).The GSM system is not an interference limited system, but a time-domain and frequency-domain limited system. Its capacity is limited by frequency (a carrier frequency of 200kHz) and time domain resources (8 TDMAs can be shared on each carrier frequency user). Therefore, the power control requirements of the GSM system are not strict. 1.9.5 Transmitter Power Control and Transmitter RF Indicators Next, let's discuss the factors that may affect the transmitter power control in the RF design.For RF, if the power detection (feedback) loop design is correct, then we can do not much for the transmitter closed-loop power control (most of the work is done by the physical layer protocol algorithm), and the most important thing is the flatness in the transmitter band.Because the transmitter calibration can only be carried out on a limited number of frequency points, especially in the production test, the less frequency points the better. However, it is entirely possible for the transmitter to work on any carrier in the frequency band in practice. In a typical production calibration, we will calibrate the transmitter's frequency points to keep accuracy. So the closed-loop power control is correct at the calibrated frequency points. However, if the transmit power is not flat in the entire frequency band, some frequency points deviates greatly from the calibration frequency point. Therefore, the closed-loop power control with the calibration frequency point as a reference will have errors and even mistakes. Ⅱ FAQ 1. What is RFID and how it works?RFID tags transmit data about an item through radio waves to the antenna/reader combination. ... The energy activates the chip, which modulates the energy with the desired information, and then transmits a signal back toward the antenna/reader. 2. What is RFID used for?RFID tags are a type of tracking system that uses radio frequency to search, identify, track, and communicate with items and people. Essentially, RFID tags are smart labels that can store a range of information from serial numbers, to a short description, and even pages of data. 3. Is RFID harmful to human?Electromagnetic fields generated by RFID devices—touted as a patient-safety technique to keep track of supplies, medical tests and samples, and people—could cause medical equipment to malfunction, according to a recent study of medical devices in Amsterdam published in the June 25 Journal of the American Medical. 4. What is RFID example?For example, an RFID tag attached to an automobile during production can be used to track its progress through the assembly line, RFID-tagged pharmaceuticals can be tracked through warehouses, and implanting RFID microchips in livestock and pets enables positive identification of animals. 5. What are the components of RFID?Every RFID system consists of three components: a scanning antenna, a transceiver and a transponder. When the scanning antenna and transceiver are combined, they are referred to as an RFID reader or interrogator. 6. Who discovered RFID?Charles WaltonRFID was, however, officially invented in 1983 by Charles Walton when he filed the first patent with the word 'RFID'. NFC started making the headlines in 2002 and has since then continued to develop. 7. How is RFID made?The antenna can be made of etched copper, aluminum or conductive ink, while the chip and antenna are typically put on a substrate that is PET or paper. ... Usually, this inlay is inserted into a printable label to create an RFID transponder that can be affixed to a product. 8. Where did RFID come from?The First RFID PatentsMario W. Cardullo claims to have received the first U.S. patent for an active RFID tag with rewritable memory on January 23, 1973. That same year, Charles Walton, a California entrepreneur, received a patent for a passive transponder used to unlock a door without a key. 9. What is a RFID system?Radio Frequency Identification (RFID) refers to a wireless system comprised of two components: tags and readers. ... Passive RFID tags are powered by the reader and do not have a battery. Active RFID tags are powered by batteries. RFID tags can store a range of information from one serial number to several pages of data. 10. What are the three parameters that define an RFID system?Every RFID system consists of three components: a scanning antenna, a transceiver and a transponder. When the scanning antenna and transceiver are combined, they are referred to as an RFID reader or interrogator. 11. What are the basic criteria in RFID?Many large organizations and government agencies have mandated that their suppliers provide goods with RFID tags. These published mandates may specify tag type, frequency, amount of memory, read range, read rate and speed, and protocol. In addition, the mandates may specify how the goods should be tagged. 12. What is the maximum read range of RFID module?Maximum read distance of 1.5 meters (4 foot 11 inches) - usually under 1 meter (3 feet) and you can use a single or multi port reader plus custom antennas to extend the read range to longer tag read distances or a wider RFID read zone. 13. What is RFID in supply chain management?+RFID (Radio Frequency Identification) is a form of extremely low-power data communication between a RFID scanner and an RFID tag. ... The tags are placed on any number of items, ranging from individual parts to shipping labels. 14. How many bits does an RFID tag have?It depends on the vendor, the application and type of tag, but typically a tag carries no more than 2 kilobytes (KB) of data—enough to store some basic information about the item it is on. Simple “license plate” tags contain only a 96-bit or 128-bit serial number. 15. Does RFID reader store data?An RFID tag can store large amounts of data additionally to a unique identifier • Unique item identification is easier to implement with RFID than with barcodes. • Its ability to identify items individually rather than generically.
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