Power Efficiency Enhancement Of Transmitters Using Adaptive Envelope Tracking And Shaping Techniques For Small Payload Space Applications
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Power Efficiency Enhancement of Transmitters Using Adaptive Envelope Tracking and Shaping Techniques for Small Payload Space Applications
With the rise of modular system architecture for distributed satellite systems with multiple small payloads instead of conventional larger spacecrafts, the efficient characterization of power budget and available power constraints become even more vital. In order to establish high data rate downlink com munications in small satellite applications, use of highly efficient, non - conventional power amplification techniques is going to be a key factor in future communication systems. The concept of having small, less power consuming and high data rate transmis sion system extends to vast number of applications like light weight Unmanned Aerial Vehicle (UAV) and hand - held communication modules etc. The idea is to study and develop an adaptive envelope tracking technique which should be able to dynamically supply power to Radiofreq uency power amplifier. Consequently, a n optimal control over system power consumption leads to enhanced efficiency. The amplifiers intended for such systems exhibit nonlinear behavior when it comes to operating at maximum output power an d cause distortion in adjacent bands. Introducing a power supply modulation block in combination with digital linearization techniques such as DPD offers considerable improvement. Th is thesis tests a dynamic power supply adaptive shaping technique f or LTE signals. In comparison to conventional fixed supply RF PAs, Envelope Tracking PA has resulted in improved linearity at the output as well as reduced unwanted power leakage into adjacent frequency channels. By imposing an isogain trajectory trough th e shaping function, we can optimize the available power for high data rate communications while keeping the intermodulation distortion at acceptable levels by considering a tradeoff between efficiency and computational load.
Bulletin of the Atomic Scientists
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Concurrent Multi-band Envelope Tracking Power Amplifiers for Emerging Wireless Communications
Emerging wireless communication is shifting toward data-centric broadband services, resulting in employment of sophisticated and spectrum efficient modulation and access techniques. This yields communication signals with large peak-to-average power ratios (PAPR) and stringent linearity requirements. For example, future wireless communication standard, such as long term evolution advanced (LTE-A) require adoption of carrier aggregation techniques to improve their effective modulation bandwidth. The carrier aggregation technique for LTE-A incorporates multiple carriers over a wide frequency range to create a wider bandwidth of up to 100MHz. This will require future power amplifiers (PAs) and transmitters to efficiently amplify concurrent multi-band signals with large PAPR, while maintaining good linearity. Different back-off efficiency enhancement techniques are available, such as envelope tracking (ET) and Doherty. ET has gained a lot of attention recently as it can be applied to both base station and mobile transmitters. Unfortunately, few publications have investigated concurrent multi-band amplification using ET PAs, mainly due to the limited bandwidth of the envelope amplifier. In this thesis, a novel approach to enable concurrent amplification of multi-band signals using a single ET PA will be presented. This thesis begins by studying the sources of nonlinearities in single-band and dual-band PAs. Based on the analysis, a design methodology is proposed to reduce the sources of memory effects in single-band and dual-band PAs from the circuit design stage and improve their linearizability. Using the proposed design methodology, a 45W GaN PA was designed. The PA was linearized using easy to implement, memoryless digital pre-distortion (DPD) with 8 and 28 coefficients when driven with single-band and dual-band signals, respectively. This analysis and design methodology will enable the design of PAs with reduced memory effects, which can be linearized using simple, power efficient linearization techniques, such as lookup table or memoryless polynomial DPD. Note that the power dissipation of the linearization engine becomes crucial as we move toward smaller base station cells, such as femto- and pico-cells, where complicated DPD models cannot be implemented due to their significant power overhead. This analysis is also very important when implementing a multi-band ET PA system, where the sources of memory effects in the PA itself are minimized through the proposed design methodology. Next, the principle of concurrent dual-band ET operation using the low frequency component (LFC) of the envelope of the dual-band signal is presented. The proposed dual-band ET PA modulates the drain voltage of the PA using the LFC of the envelope of the dual-band signal. This will enable concurrent dual-band operation of the ET PA without posing extra bandwidth requirements on the envelope amplifier. A detailed efficiency and linearity analysis of the dual-band ET PA is also presented. Furthermore, a new dual-band DPD model with supply dependency is proposed in this thesis, capable of capturing and compensating for the sources of distortion in the dual-band ET PA. To the best of our knowledge, concurrent dual-band operation of ET PAs using the LFC of the envelope of the dual-band signal is presented for the first time in the literature. The proposed dual-band ET operation is validated using the measurement results of two GaN ET PA prototypes. Lastly, the principle of concurrent dual-band ET operation is extended to multi-band signals using the LFC of the envelope of the multi-band signal. The proposed multi-band ET operation is validated using the measurement results of a tri-band ET PA. To the best of our knowledge, this is the first reported tri-band ET PA in literature. The tri-band ET PA is linearized using a new tri-band DPD model with supply dependency.