Next-generation base station radio frequency architecture

Abstract

Base station costs are dominated by the cost of radio frequency (RF) macrocell will therefore no longer be the dominant type of infrastructure equipment. As a result, costeffective scalability in terms of output power and traffic capacity therefore becomes an absolute necessity.New trends in spectrum regulation are appearing, such as the allocation of analog television (TV) spectrum for mobile communication, and dynamic spectrum usage techniques through cognitive radio approaches. These trends mandate a higher level of flexibility from infrastructure equipment in terms of frequency agility and will require spanning wide frequency ranges from 450 MHz to 5400 MHz. IntroductionThe base station type most often used in wireless communication networks is the classical macrocell shown in Figure 1. However, there is increasing interest in alternative architectural approaches for different deployment scenarios. Microcells are used to fill coverage gaps. Radio frequency (RF) heads connected to base station hotels via fiber allow for collocating multiple base stations. Furthermore, home base stations are gaining more attention from service providers that want to move subscribers from fixed line to wireless equipment. Femtocells are being considered for providing service in planes or on ships. In the future, the classical by shrinking the size of filters, power amplifiers, and cooling will also turn into OPEX savings as less real estate is required. State-of-the-Art Base Station TechnologyWhat technological advances are necessary to reduce costs, form factor, weight, and energy consumption of infrastructure equipment?The base station in Figure 1 indicates that a quarter of the form factor is dominated by the duplex filters. These split the antenna signal into the receive and transmit paths. Furthermore, an additional half of the form factor is occupied by power amplifiers and cooling equipment. Radio and baseband cards occupy only a minor fraction of the base station's volume. Over the years, the breakdown of the form factor described has remained substantially the same. This is because baseband and low-power RF processing follows Moore's law, but high-power RF does not. Duplex filters need to provide high selectivity. Therefore, high quality (Q) factors, which require large energy storage and hence a large form factor, are needed. Furthermore, resonator dimensions are tied to the wavelength. As a result, today's filter approach will not lead automatically to smaller dimensions over time. A new filter concept is necessary. Figure 2 provides a detailed schematic of the power budget of a base station. The power amplifiers (PAs) dominate the power consumption. The effective usable power amplifier efficiency, including all predriver stages, RF cabling, and filtering, is only 4 percent (20 W͞490 W). Nearly half of the power (6 kW) drawn from the mains line is dissipated by the PAs (2.8 kW). The overall efficiency when relating RF power to mains power is only 1.9 percent (6 * 20 W͞6184 W). A significant improvement in efficienc...

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