Current and evolved physical layer concepts : potentials and limitations of mobile broadband wireless access
Two important factors fuel the fast evolution of mobile broadband access technologies: The ever-increasing demand for high data rates due to the availability and acceptance of mobile devices and applications and the demand for affordable broadband access in under served areas where radio technologies are regarded as a substitute to fixed line technologies. This thesis highlights potentials and limitations of current and future mobile radio systems for area-wide mobile broadband access. It describes and thoroughly analyzes the physical layer of the current Release 8 of the UMTS LTE mobile radio standard implemented as single-antenna system. Different novel modifications and alternative concepts are introduced and analyzed which aim at either increasing the physical layer performance or at decreasing the computational complexity. In addition, upper bounds on the performance concerning the obtainable bits per channel use are regarded for single- and multiple-antenna systems. It is observed that single-antenna LTE operates at approximately 65% of the Shannon limit. On top of the physical layer simulation results, system-level simulations of the downlink in a cellular environment are performed to evaluate the potentials and limitations of UMTS LTE and the introduced physical layer modifications concerning the coverage, quality and capacity of a radio cell within a mobile radio network. Two carrier frequencies are considered: 0.8GHz and 2.0GHz representing the frequencies from the digital dividend and of current UMTS deployments, respectively. The employed frequency bandwidths of 5MHz and 20MHz represent the frequency bandwidth of current UMTS and the largest frequency bandwidth supported by UMTS LTE Release 8, respectively. Additionally, different propagation scenarios representing typical mobile radio environments are considered. System-level simulation results reveal an imbalance concerning the individual user goodputs (error-free throughput) within a radio cell: near the cell edges these individual user goodputs might drop to only one tenth of the user goodputs that are achieved near the base station. The average cell goodput is derived and given for all combinations of the considered system-level parameters. It is shown that the achieved goodputs scale linearly with the available frequency bandwidth. The influence of the carrier frequency is observed to significantly influence the coverage and capacity of a radio cell only if it is interference limited. In the future, major gains can be expected from more sophisticated coding and signal processing. The most promising options are multiple-antenna systems and intelligent interference management algorithms. With the derived bounds it is shown that in theory, a capacity achieving 4×4 multiple-antenna system using 20MHz frequency bandwidth and ideal interference cancellation could achieve an average cell goodput > 1Gbit/s.
info:eu-repo/classification/ddc/620, UTRA, LTE, OFDM, Ingenieurwissenschaften, physical layer concepts, UMTS LTE, spectral efficiency
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