As a final part RRU unit for wireless communication, the key device, like an air bridge to provide reliable channels for the exchange of user information, to ensure that the information is accurate, real-time delivery. The RRU bundle of baseband digital signals by a complex, delicate converting circuit, converted into radio waves by the antenna out; the same time, receiving the information sent by the user terminal, to the core network to complete the information exchange.
RRU What are the key technology? RRU key indicators affecting the performance of what? In this paper this simple analysis.
Typical internal RRU generally consists of four components: a power supply unit, a transceiver unit, a power amplifier unit, the filter unit (see FIG. 1). The external interface are: power input port, optical input / output port, antenna interface electrically reconcile dry contact interface. Power supply portions are provided, reception signal processing, power amplification, transmit and receive filtering function key.
For more RRU performance evaluation dimensions, volume / weight, the whole power output, the number of channels the whole, the whole energy consumption ratio, the whole radio frequency indicators are evaluated dimension options, only to meet customer needs RRU, is good product. When the focus is not the same customer needs, choose a different dimension. For a RRU, at the same power level, the same number of channels premise, the key technology determines its core competence: the whole energy than RF specifications.
The total power and input power ratio of energy consumption is the output of the RRU, the index reflects the key technology of RRU: CFR algorithms, TRX hardware design capability, power amplifier design capabilities.
Under certain conditions the input power, the higher the ratio of energy RRU machine, the machine described heat consumption is relatively small, with a small heat RRU teeth to complete cooling, the temperature rise protection reliability requirements; these same techniques the application which makes miniaturization possible. RRU system in order to reduce overall power consumption, PA (power amplifier) is an important component, which accounts for more than 65% of the power consumption of the machine. Changes in PA efficiency of heat consumption of the machine, the power consumption is very large impact, improve PA efficiency become a key technology PA design.
PA efficiency gains
PA module for ZTE RRU, we continue to optimize multi-way Doherty technology, single-band PA efficiency up to 50%, multi-band PA efficiency up to 45% currently on the maturity scale applications at the forefront of the industry.
In a wireless communication system, is an important indicator EVM (Error Vector Magnitude), particularly in 4G, 5G communication systems commonly used in high-order modulation scheme. In order to ensure wireless transmission signal EVM output power, the ACPR (adjacent channel power ratio), PA requires a high saturation power headroom, it must be more PA power back-off, resulting in severely reduced efficiency of the PA . It would appear that protect and enhance PA efficiency EVM seems to be a contradiction of indicators demands.
ZTE's software engineers by CRF, continuous optimization DPD software algorithms to effectively solve the contradiction EVM, ACPR and efficiency of the PA.
● on the radio transmission signal EVM modest peak cut process, reducing the PAPR of the output signal, to reduce the output back-off amount of PA, PA ensure a higher efficiency. We CFR unique algorithm reduces the maximum PAPR signals, while minimizing the amount of EVM deterioration of the transmitted signal, to ensure the integrity of the whole RRU transmit signals.
● DPD transmission signal by predistortion processing, the adjustment of the input signal spectral component, the phase characteristic parameters, so that the predistortion signal input passes through nonlinear circuit PA, will produce nonlinear superposition correction, the final output signal ACPR is required to meet the system. ZTE RRU DPD technology ACPR improvement of up to 30dB above, in the industry's first array.
ZTE constant pursuit of the perfect upgrade power amplifier design and performance of the algorithm, currently studying a new generation of technology to enhance the efficiency of the PA, including the envelope tracking (ET) technique and constant envelope amplification technology (Outphasing).
TRX key technologies
TRX core veneer for the RRU, mainly to complete data interaction with the BBU, and transmitting a data exchange between the RRU, radio / reception of signals, monitoring and management of the key module's internal RRU. TRX power accounts for more than 15% RRU overall heat consumption.
TRX hardware core technologies include:
● highly integrated digital circuits, multi-functional, low power consumption;
● Multi-channel RF integrated circuit, the receiving circuit high linearity, low noise, high dynamic design; low power consumption.
TRX software core technologies include:
Dynamic power control ●: dynamic carrier configuration, arranged according to the real-time adjustment of the optimum power RRU business machine, reduce power consumption at low traffic machine;
● DPD performance capabilities; higher processing bandwidth carrier; supports multi-mode multi-carrier peak clipping capability, especially to support G / U / L / NB / NR multimode, mixed multi-carrier configuration; carrier comprising handle more receive, transmit channel capability.
● PIMC Function: passive intermodulation occurs due to the interference signal generated, through PIMC function, will fall in the received frequency interference RRU device automatically filtered.
Filter key technologies: transmitting channel low insertion loss high rejection of
The larger the transmit channel filter insertion loss, the greater the power loss by the transmission, the transmission channel is increased insertion loss 0.1dB, PA efficiency loss equivalent to a percentage. Generated by the filter insertion loss of about 10% of the heat consumption overall heat consumption.
In order to protect the transmission channel filter insertion loss in the case of band rejection indicators to meet the constant reduction, usually TE mode dielectric resonators, metal to replace the TEM mode resonator. Q value of the dielectric resonator is very large, typically 10,000 or more can be done, the value of 4000 compared to a metal resonator, much higher. In the design, a smaller number of dielectric resonators to achieve the same suppression requirements, thereby reducing the transmit channel filter insertion loss, but also enhance the capacity of the power diplexer.
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Power key technologies: high efficiency
Refers specifically to a board power supply provided RRU machine, which is responsible for the external power supply, through mine, after filtering, the conversion process, the conversion power based on an internal board of each RRU module can be used. Veneer less power type, current is large, such as -48V PA unit, 28V power supply, transceiver 5.5V power supply.
The use of DC / DC isolation architecture, a comprehensive power efficiency of about 93%.
The use of DC / C non-isolated architecture, its overall efficiency is expected to reach 94.5%.
Power consumption of a thermal machine comprises from about 10% RRU heat consumption, the fine design of the RRU, the portion of the heat consumption can not be ignored, to be better, as far as possible to improve efficiency.
RRU of the heat dissipation key technologies
Cooling machine RRU has active cooling and natural cooling in two ways.
Active cooling, the RRU mainly refers to the air-cooling mode, the fan or other device using the driving surface RRU fast flow of air, the cooling heat accumulation RRU tooth surface flash away, thereby reducing the internal temperature RRU. In this manner, heat dissipation can be greatly reduced RRU teeth area, thereby reducing size and weight reduction. ZTE according to customer demand, a low noise active cooling solutions, can provide more than 110W / L cooling capacity, which greatly reduces the volume of the RRU machine.
Natural cooling means according to rising hot air RRU natural law by the heat of the power generated by itself binding the external environment, complete the radiation of heat, reduce internal temperature. Rely on natural cooling, requires RRU must have sufficient heat dissipation area protection. ZTE natural cooling, for a long accumulation, the maximum capacity of the natural cooling RRU reached 52W / L, is leading the industry.
ZTE RRU covering multiple frequency from the single frequency bandwidth from narrow to wide bandwidth and more from Massive MIMO 2T2R product to a Port 2, forming a complete product line in the FDD and TDD fields. High efficiency, low power consumption technology application, so that the same power output, small size RRU machine, light weight. Application of new technologies, such RRU in the same volume, with higher power output, provide more coverage of the carrier and greatly enhance the quality of the network clients.
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