Cell Capacity Analysis of Relay Enhanced LTE-A Systems
Author(s): Chen, Y.
Chair of Communication Networks (ComNets), Faculty 6, RWTH Aachen University
Contact: publications@comnets.rwth-aachen.de
Ph. D. Dissertation
, ABMT
76
,
p.
204
, ISBN: 978-3-95886-429-0
Wissenschaftsverlag Mainz,
Year: 2020
On page(s):204
ISBN: 978-3-95886-429-0
Abstract Cellular digital broadband mobile radio systems of the 3rd Generation Partnership Project (3GPP) Long Term Evolution- Advanced (LTE-A) standard (4th generation) were supplemented with a new network element in Release 10: fixed Relay Nodes (RN) operating on Layer 2 of the International Organization for Standardization/Open Systems Interconnection (ISO/OSI) model. Since their invention by ComNets in 1999, RNs have been researched worldwide. They improve the radio signal received by Mobile Stations (MS) in mobile radio cells and, if deployed properly, increase cell capacity and spectrum efficiency. Present results, which characterize mean values of performance parameters for relay enhanced cells, are based on evaluations with event-driven stochastic system simulation. Although these simulators of equipment vendors and network operators represent the systems in great detail, results known from 12 companies on the performance of RNs show very different findings. The simulation models are obviously not comparable to each other in terms of quality and assumptions. There is no transparent analysis method to calculate important performance parameters of relay enhanced LTE-A systems. This work faces up to this task and solves it very convincingly. In a first important contribution the work develops a mathematical model, taking into account all parameters and radio propagation models given by International Telecommunication Union Radiocommunication Sector (ITU-R) for the evaluation of LTE-A systems for a Urban Macro-cell (UMa) scenario. It calculates the distributions of Signal to Interference plus Noise Ratio (SINR), error rate, throughput and spectrum efficiency depending on the location of a MS for each small 5 * 5 m area element of a multi-cell mobile radio network for the downlink (DL). The model takes into account the physical transmission properties of the radio channel, Adaptive Modulation and Coding (AMC) and corresponding error rates by calculating throughput. It also models the functions in Layer 2 of the ISO/OSI model, namely the Hybrid Automatic Repeat Request (HARQ) protocol running in the Medium Access Control (MAC) sublayer and the Selective Repeat Automatic Repeat Request (SR-ARQ) protocol performed in the Radio Link Control (RLC) sublayer above MAC, where transmission errors of protocol control information and the number of allowable retransmissions of a user data block are also taken into account. In relay enhanced systems two sequential radio links are operated, each based on the protocols mentioned above. The distribution of successfully transmitted packets or their consumed radio resources results in the throughput distribution of the location-dependent area element. Summing up over all area elements results in the throughput distribution or the spectrum efficiency on DL of the cell. Thereby the protocol stack for radio transmission of IP packets is fully taken into account. Multiple transmissions of the same user data, which occur with probability, possibly also through lower-lying protocol layers in the protocol stack, lead to unclear mathematical expressions for resource consumption. This work uses Signal Flow Graphs (SFG) known from literature to simplify the mathematical expressions and make them comprehensible. A smaller contribution of the dissertation concerns systematic investigations of spectrum efficiency with different partition of radio resources of a cell on direct (BS <-> MS), backhaul (BS <-> RN) and access link (RN <-> MS). The optimal partition is presented; it avoids bottlenecks in traffic theory. It is worthy of note that most of the cell’s traffic runs via RNs and the variance of the user throughput becomes minimal. This work parameterizes the presented model just as in a dissertation (K. Sambale) completed previously at ComNets, which uses simulation to optimize the number and locations of RNs per cell in order to maximize cell capacity and spectrum efficiency. This work succeeds in validating the mean values of its own results against the results of the work mentioned above and a simulation work published by Nokia employees. This work also investigates the case, that pico cells (as out-of-band RNs or with cable connection) are deployed instead of RNs at their locations. Since in this case no resources are required for the backhaul link, the system capacity of a cell doubles. The computational effort for a certain parameter set to characterize the studied 800 * 800 m service area is about 10 days on a 64-PC-cluster. On DL other BSs make interference, while on uplink (UL) interferers are all MSs. Because the number of MSs is substantially larger than that of BSs, statistically trustworthy simulation results require an enormous amount of computational effort, which no one has yet invested. The presented method is also suitable for calculating throughput, capacity and spectrum efficiency on UL for cells with and without relays. This is a third particularly important contribution of the work. In order to model the interference from MSs, a cell is partitioned into divisions with exclusively allocated radio resources. The partitioning is chosen in the multi-cell radio network in such a way that co-channel interference appears at locations that are geometrically as far away as possible. Divisions with the same radio resources are arranged in a regular pattern across all cells. Multiple divisions of the same cell can be grouped into a partition, where the traffic-theoretical trunking gain increases compared to that of individual divisions. In the case with BS only, this model results in a fairly even distribution of SINR or spectrum efficiency over small area elements across the system. Compared to a non-partitioned cell, the spectrum efficiency with partitioning increases only slightly, but the standard deviation decreases significantly. Therefore, MSs can be served fairly equally regardless of their locations in the cell. For UL of relay enhanced cells it is shown in an exemplary way with a parameter set, that relays can distinctly increase the spectrum efficiency on UL.
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Bibtex
@PHDTHESIS{DissChen2020
AUTHOR = {Chen, Y.} ,
TITLE = {Cell Capacity Analysis of Relay Enhanced LTE-A Systems} ,
YEAR = {2020} ,
MONTH = {Dec} ,
VOLUME = {76},
PAGES = {204},
PUBLISHER = {Wissenschaftsverlag Mainz},
ADDRESS = {Communication Networks (ComNets) Research Group @ RWTH Aachen University},
SERIES = {ABMT},
AFFILIATION = {Chair of Communication Networks (ComNets), Faculty 6, RWTH Aachen University},
ISBN = {978-3-95886-429-0 },
URL = {https://www.comnets.rwth-aachen.de}