OFDM physical layer architecture and real-time multi-path fading channel emulation for the 3GPP long term evolution downlink
Briggs, Elliot S
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This dissertation is focused on OFDM receiver algorithms, particularly involving receiver synchronization and channel equalization. These two topics are critical components in an LTE downlink receiver. The various aspects of receiver synchronization are presented and their impact on reception quality is quantitatively defined. Building on this information, a receiver architecture is constructed that is capable of simultaneously correcting symbol timing and sampling frequency offset using a feedback-controlled arbitrary-ratio resampler. The topic of channel estimation is presented by first investigating MMSE algorithms, leading to the more practical family of algorithms that use stochastic optimization techniques. A new family of algorithms is explored that are based on locally weighted linear regression. The regression algorithm uses an optimum parameterized kernel, found using offline training. Throughout the dissertation, algorithms are tested using realistic models that emulate typical time-varying multi-path fading channel scenarios defined by the LTE standard for conformance testing. To perform extended simulations in real-time, a channel emulator architecture is developed, implemented, and tested in FPGA hardware. The developed architecture allows online programming of the desired spatial and temporal correlation properties of the channel and has been designed to be scalable to the desired spatial or temporal dimensions. The primary goal of the dissertation is to offer high performance, while maintaining a low complexity, cost-effective hardware implementation. Although implementation details target an FPGA-based design, the concepts can be extrapolated to ASIC or even software-based targets.