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Mobile and Wireless Communications Network layer and circuit level design 2012 Part 12

Tham khảo tài liệu 'mobile and wireless communications network layer and circuit level design 2012 part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 16 Power Amplifier Design for High SpectrumEfficiency Wireless Communications Steve Hung-Lung Tu Ph.D. Fu Jen Catholic University Taiwan 1. Introduction The growing market of wireless communications has generated increasing interest in technologies that will enable higher data rates and capacity than initially deployed systems. The IEEE 802.11a standard for wireless LAN WLAN which is based on orthogonal frequency division multiplexing OFDM modulation provides nearly five times the data rate and as much as ten times the overall system capacity as currently available 802.11b wireless LAN systems Eberle et al. 2001 Zargari et al. 2002 Thomson et al. 2002 . The modulation format of the IEEE 802.11a is OFDM Orthogonal Frequency Division Multiplexing which is not a constant-envelope modulation scheme more sensitive to frequency offset and phase noise and has a relatively large peak-to-average power ratio. These reasons induce the linearity requirements which are crucial for power amplifier design. Among various linearization techniques transistor-level predistortion is the simplest approach to implement and can be realized in a small area which makes it be the most compatible with RFIC implementation. Conventionally WLAN has been implemented with multi-chip approach or single chip with processes other than CMOS. For example the radio frequency RF and intermediate frequency IF sections are fabricated with GaAs or BiCMOS processes and the baseband DSP section with a CMOS process. Note that the complexity and cost will be dramatic in a wireless LAN system with hybrid processes which makes the CMOS process be the most promising approach to achieve high integration level low power consumption and low cost for the integration of baseband and RF front-end circuits of a WLAN system. There are two different modulation schemes employed in wireless communication standards linear modulation and nonlinear modulation in which the former one is employed in North American Digital .