Application of RF technology in wireless communication

JasonYoo

Application of RF technology in wireless communication [Copy link]

What is Radio Frequency? Radio Frequency, or RF for short, is radio frequency current, which is the abbreviation of a high-frequency alternating electromagnetic wave. Alternating current that changes less than 1,000 times per second is called low-frequency current, and alternating current that changes more than 10,000 times per second is called high-frequency current. Radio frequency is such a high-frequency current. Radio frequency technology plays a wide and irreplaceable role in the field of wireless communications.

JasonYoo

Bluetooth radio frequency technology Bluetooth wireless technology uses a digital coding technology that expands the spectrum of narrowband signals. Through coding operations, the number of transmitted bits is increased and the bandwidth used is expanded. Bluetooth uses frequency hopping to expand the spectrum. Frequency hopping spread spectrum reduces the power spectrum density of the signal on the bandwidth, thereby greatly improving the system's ability to resist electromagnetic interference and crosstalk interference, making Bluetooth wireless data transmission more reliable. In terms of frequency band and channel allocation, the Bluetooth system generally operates in the 2.4GHz ISM band. The starting frequency is 2.402GHz, the end frequency is 2.480GHz, and a 2MHz protection band is set at the low end and a 3.5MHz protection band is set at the high end. All Bluetooth units sharing a common channel form a micronet, and each micronet can have up to 8 Bluetooth units. In the micronet, the clocks and frequency hopping of each unit on the same channel are synchronized. Bluetooth has the following RF transceiver characteristics. Bluetooth adopts a time-division duplex transmission scheme, using one antenna to send and receive signals at different time intervals, and sharing a channel by constantly changing the transmission direction when sending and receiving information, to achieve full-duplex transmission; Bluetooth transmission power can be divided into three levels: 100mW, 2.5mW and 1mW. The generally used transmission power is 1mW, the wireless communication distance is 10m, and the data transmission rate is 1Mb/s. If the new Bluetooth 2.0 standard is adopted, the transmission power is 100mW, which can make the Bluetooth communication distance reach 100m and the data transmission rate reach 10Mb/s. In addition, the Bluetooth standard also makes detailed provisions for parasitic radiation, radio frequency tolerance, interference and out-of-band suppression in the transceiver process to ensure the security of data transmission. Bluetooth wireless devices realize serial communication through wireless radio frequency links, which are realized by using Bluetooth modules. The Bluetooth module is mainly composed of three units: wireless transceiver unit, link control unit and link management and host I/O. As for the Bluetooth RF module, in order to improve the transceiver performance while reducing the size and cost of the device, each company has adopted some of its own unique technologies, so that the structure of the Bluetooth RF module is different. But in terms of its basic principle, the Bluetooth RF module is generally composed of three modules: the receiving module, the transmitting module and the synthesizer. Among them, the synthesizer is the most critical part of the transceiver module. The synthesizer uses phase-locked loop technology in channel selection and receiving mode. In the receiving mode, the phase-locked loop is closed to provide the stable local oscillator required for the demodulation signal of the receiving module. In the transmitting mode, the phase-locked loop is open, and the modulated signal is directly loaded onto the VCO to modulate the carrier. At this time, the carrier frequency is maintained by the output voltage of the loop filter. Usually the operating frequency of the synthesizer is only half of the transmitting frequency to reduce coupling with the RF amplifier.

JasonYoo

Next Generation WLAN Radio Technology First generation WLAN solutions have limited ability to react to changes in user density and are not able to effectively optimize bandwidth resources. As WLAN load increases, existing products are often unable to determine whether the load of adjacent access points is similar to the number of users, nor can they determine whether it is necessary to share the load with adjacent access points. User load balancing requires the use of more centralized software control, which can be used to perform system-level network efficiency assessments to optimize the ratio of users to access points. Next generation systems will fully utilize the entire software framework to detect access point failures and automatically adjust based on the working conditions of nearby access points. By controlling the output transmit power and operating frequency of each access point, the system can allow specific access points to fill in possible coverage gaps by increasing power or changing channels, or to reduce mutual interference between access points, thereby increasing network stability. Furthermore, if an access point fails, the system can instruct specific access points to share certain clients to optimize communication routing and network load. Finally, access points can know what is happening around them and can detect gaps in range. Because RF coverage patterns cannot be predicted, system availability can be greatly affected by seemingly harmless behavior, such as the movement of an elevator. While many organizations shy away from systems that are too adaptive, increasing the output power allows the system to detect and patch vulnerabilities in range, which can also provide other benefits such as increased network uptime. When considering the scalability of wireless networks, it is also helpful to have a comprehensive understanding of the RF domain. The next generation of access points will be able to provide dual-band connectivity, including 802.11b, 802.11g, and 802.11a. With limited available spectrum such as 2.4GHz and 5GHz frequencies, the goal of any network design should be to optimize the use of available channels and provide the maximum amount of bandwidth to each client. The RF medium plays a distinct role in the overall security of a wireless network. Although the physical layer is not responsible for device and user authentication or for encrypting data packets that travel over the air, it can provide important data about unauthorized access points or suspicious client device behavior. Although there are many detection solutions on the market, most products are configured to cover the entire network rather than integrating it into a single system. Wireless access points should be able to operate in detection mode to determine whether other wireless components are configured correctly. They should also be able to report which access points or client devices have not been approved by the ITO. Ideally, the RF implementation of this wireless detection should be supplemented by a wired implementation and have the ability to correlate suspicious behavior detected in the wireless network with information collected in the wired environment. Through this correlation capability, the system can determine whether the suspicious access point belongs to a host network or is just part of the infrastructure of a neighboring enterprise. In addition, by continuously monitoring network behavior, the system can perform intrusion detection and prevention functions and report on rogue access points, ad hoc networks, denial of service attacks, and man-in-the-middle attacks.

JasonYoo

RF Management in Network Optimization When optimizing a network, we must ensure that there is no overlap when transmitting energy. This is especially important for each cell of a CDMA system using the same frequency. RF management is about ensuring that RF energy is transmitted without causing any pollution - getting the energy where it is needed and away from where it is not needed. Therefore, it is very important to suppress the antenna side lobes and back lobes and adjust the antenna coverage by adjusting the electrical tilt angle. The smaller the cell, the more important it is. Studies have shown that the impact of interference is related to the suppression of the antenna upper lobe. When seeking to reduce the interference level, suppress the antenna upper lobe as much as possible. In the past, the suppression of the upper lobe was usually within 12dB, but now the target suppression has reached 18-20dB. RFS's Optimizer series antennas have achieved suppression of more than 20dB across the entire tilt range. The smaller the side lobe is relative to the main lobe, the stronger the antenna's ability to resist co-channel interference. If the interference is not caused by the first upper lobe, it may be the second upper lobe, so each unwanted signal must be as small as possible. Electrical tilt adjustment is a major advantage in cell planning and management of modern mature networks. Mechanically adjusting the antenna beam is easy to operate, but it has little effect on the radiation of spurious side lobes and may even increase interference from the back lobes. Electrical tilt adjustment technology can tilt all main lobes, back lobes and side lobes to the same angle. In other words, electrical tilt adjustment technology can manage the radiation of side lobes at different tilt angles to enhance interference control. Remote antenna tilt control technology mainly refers to the ability to control the antenna tilt from other locations other than the top of the antenna tower. Remote tilt control has many advantages: no need to pay for renting equipment to climb the antenna tower; avoidance of impact on other operators with base stations in the same location, etc. It can help operators dynamically adjust the network according to changes in business traffic patterns throughout the day, which is another basic feature of multi-functional high-performance antennas.

JasonYoo

Ultra-Wideband (UWB) Wireless TechnologyUltra-Wideband (UWB) is a wireless radio frequency technology that enables home appliances, computer peripherals, and mobile devices to transmit data at high speeds over short distances with very low power consumption. The technology is ideal for wireless transmission of high-quality multimedia content. UWB technology uses a wideband wireless spectrum to transmit data over short distances (such as within a home or small office), allowing it to transmit more data wirelessly in a given period of time than traditional wireless technologies. This feature, combined with low-power pulsed data delivery, speeds up data transmission while not being affected by interference from other existing wireless technologies such as Wi-Fi, WiMAX, and cellular wide-area communications. Impulse Radio (IR) is one of the most promising ultra-wideband technologies. IR signals consist of very narrow pulses that occur pseudo-randomly in time. Pseudo-randomness is achieved by time-hopping codes, which randomize the transmitted signal to facilitate user separation and spectrum shaping to avoid eavesdropping. The signal can be modulated using pulse amplitude modulation (PAM) or pulse position modulation (PPM). To ensure low-cost ultra-wideband devices, all pulses have the same waveform. Compared with existing wireless communication technologies, the communication carrier used by UWB wireless communication technology is a continuous radio wave. Figuratively speaking, this radio wave is like a person holding a hose to water the lawn, and the water in the hose forms a continuous water flow fluctuation as the hand moves up and down. Almost all wireless communications, including mobile phones and wireless LAN communications, are like this: the signal is loaded on a continuous radio wave using some modulation method. In comparison, UWB wireless communication technology is like a person using a rotating sprinkler to water the lawn, which can spray more and faster short water flow pulses. UWB products can send a large number of very short and very fast energy pulses when working. These pulses are precisely timed, each only a few nanoseconds long, and the pulses can cover a very wide area. Ultra-wideband technology brings an advantage that the circuit is simpler, especially at the receiving end, because there is no need to generate the carrier locally, nor is it necessary to provide multi-stage hybrid circuits, shaping filters, etc. However, the advantages brought by using carrier spread spectrum outweigh ultra-wideband technology. Ultra-wideband itself is a type of baseband signal (although its spectrum range reaches several GHz). In this case, the propagation characteristics of the near-DC and mid-range parts of the spectrum have different characteristics, which limits this technology to short-distance communications. For long-distance communications, especially relaying, spread spectrum technology is more suitable.