In this paper, we analyze the symbol-error rate of a two-hop fixed-gain amplify-and-forward OFDM relay network when nonlinear distortion, as a consequence of relay amplifier saturation, is considered at the relay. We begin by constructing a theoretical model of the system. Due to the Gaussianity of OFDM waveforms, we are able to employ Bussgang's theorem in our model, which enables the calculation of a closed form expression for the SER. From our theoretical analysis, we can calculate the optimal relay gain that should be applied to minimize the symbol error rate. We demonstrate the performance gain achieved through the application of the optimal relay gains through both numerical simulations and real-world experimentation using a USRP relay network testbed.
-This paper presents results from a novel OFDMA multi-cell mobile broadband system level simulator. The tool is used to statistically characterize uplink and downlink inter-cell interference. Without suitable interference management, multi-billion dollar networks can collapse under the strain of heavy traffic loads. Fully loaded interference studies cannot be performed on the network until it has been fully deployed. As such, interference analysis and management must be accurately performed pre-deployment using detailed network simulators. System level simulation is a highly computationally intensive procedure. This paper discusses the simulator architecture (and steps taken to reduce computational complexity) and then demonstrates the impact of inter-cell interference in OFDMA networks. In an interference limited scenario the results demonstrate that it is the frame-to-frame fluctuations in interference, and not the received signal level, that dominate inaccuracies in the Channel Quality Index (CQI) prediction. CQI is used in the fast link-adaptation process to select the MCS mode for each user on a frame-byframe basis. Results show that incorrect Modulation and Coding Scheme (MCS) modes are chosen up to 40% of the time when the CQI is delayed by 3 frames and the user is interference limited. Perfect MCS selection is then shown to improve user throughput by up to 50%.
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