Since Long-Term Evolution (LTE) commercial network has introduced, the user's mobile Internet experience has changed. Get high-quality video content wherever and whenever you need it, and get popular social network services with fast and easy Internet connectivity. In addition, the demand for higher video quality and larger smartphone displays increases mobile data traffic. According to the Cisco Visual Networking Index (VNI) released in 2017, worldwide mobile data traffic is expected to grow 63% in 2016 and sevenfold in 2016-2021. According to VNI, 4G traffic accounts for 69% of total traffic, while 4G connections represent only 26% of mobile connections in 2016, but mobile networking technology advances will result in a rapid increase in mobile data traffic per connection. In order to cope with such explosive mobile data traffic, mobile network operators will increase the spectrum bandwidth of LTE Advanced and LTE-Advanced Pro, and among the advanced technologies such as Carrier Aggregation (CA), Device-to-Device Communications and Cooperative MultiPoints provide greater capacity expansion by consolidating multiple component carriers for higher data rate transmission in discrete spectrum bands.
CA applied to Korea's commercial cellular network in mid-2013. However, CA performance in commercial networks has not been well studied yet. Therefore, this paper shows how CA technology is applied to a commercial network and how it is performed. Extensive drive field testing has been conducted to compare the performance of CA technologies and non-CA technologies in high-density urban and sub-urban areas using commercial eNBs and UEs. A downlink (DL) CA with a 2-component carrier (CC) of 30 MHz aggregate bandwidth (BW) was used in the network with a CC of 20 MHz BW in band 7 and one CC in band 5 to 10 MHz BW. Measurements During the sub-city drive test, the CA's maximum DL data rate was close to the theoretical peak transmission rate of 225 Mbps, reaching 203 Mbps and confirming that the average DL data rate was 76 Mbps. For comparison, the maximum DL data rate for a single carrier Band 7 was 141 Mbps and the same DL data rate was 51 Mbps.
However, the CA throughput level accounts for 97% and 96.6% of the sum of the two single-carrier throughputs for cities with high-density cities and sub-cities. In our analysis, this performance degradation is due to a lack of support for flexible PCell-SCell configurations using measurement event A6. The CA needs a very fast connection between the various MAC layer entities of the CC involved in the CA operation. Because this high-speed connection was not supported between different eNBs at the time of the drive test, the CA between two bands belonging to different eNBs was not possible. Also, one PCell can be mapped to only one SCell, even if the adjacent cell has better conditions than the current SCell. In this context, this paper proposes a load-aware Secondary Serving Cell (SCell) change algorithm for LTE-Advanced Carrier Aggregation (CA) system to improve cell edge performance. We found that the standardized SCell change algorithm had performance drawbacks because the actual measurement data was analyzed and event A6 was used only based on RSRP (Reference Signal Received Power) measurements. To this end, the proposed algorithm utilizes the signal-to-interference-and-noise ratio (SINR) and user throughput estimates of available physical resource blocks (PRBs) for SCell change decision. System-level simulation results show approximately 11% performance improvement in high-density urban scenarios compared to event A6-based SCell change algorithms.
