The mobile network operators (MNOs) are looking into economically viable backhaul solutions as alternatives to fiber, specifically the hybrid fiber coaxial networks (HFC). When the latencies from both the wireless and the HFC networks are added together, the result is a noticeable end-to-end system latency, particularly under network congestion. In order to decrease total system latency, we proposed a method to improve upstream userto-mobile core latency by coordinating the LTE and HFC scheduling in previous papers. In this paper, we implement and optimize the proposed method on a custom LTE and DOCSIS end-to-end system testbed. The testbed uses the OpenAirInterface (OAI) platform for the LTE network, along with Cisco's broadband router cBR-8 that is currently deployed in the HFC networks around the world. Our results show a backhaul latency improvement under all traffic load conditions.
Consumer demand for rich content delivered to portable wireless devices is pushing the wireless industry and researchers to find ways to improve the efficiency of wireless networks. New technologies like LTE and LTE-Advanced are being refined and deployed to meet demands. This thesis studies three important areas of wireless communications using LTE; phase noise, Doppler and link adaptation and the performance of various multiple antenna systems. The thesis focuses on the performance of 4 base station antennas and results obtained with the advanced 3 rd Generation Partnership Project's (3GPP) extended spatial channel model (SCME). Simulations show the effect of each impairment and configuration on the LTE physical downlink shared channel. The best performing antenna configuration evaluated is the 4-transmitter, 4-port, correlated cross-polarized BS antenna when TM4's closed-loop spatial multiplexing is used. The results show that a 4 antenna BS setup provides gain over 2 BS antennas, despite the additional reference signal overhead, due to the greater set of precoding matrices available with 4 antenna ports. When only 2 ports are available, TM3's open-loop spatial multiplexing (OLSM) performs better than TM4 as the user equipment (UE) becomes mobile, since 2-port TM3 is less dependent on the channel state information. The practical implementation issues of link adaptation are shown to cause a significant drop in throughput at medium and high UE velocities. The results in the thesis suggest that improving the latency of the link adaptation loop with low complexity algorithms, or an increase in processing power, along with adaptive link adaptation reporting intervals can keep uplink overhead low and maintain a higher throughput as velocity increases. The UE velocity is also pushed to extremes in the high speed train on railway simulations and shows that LTE can operate with some throughput degradation at 350 km/hr. Finally, the LTE downlink is also subjected to phase noise; an important impairment present in communication systems employing up/down-conversion. The generated phase noise and the measured phase noise simulations show the effect of phase noise on the throughput. As expected, the relatively quiet measured phase noise does not significantly degrade the LTE downlink.
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