Takeshi Nakamori

Investigation on Mobility Management for Carrier Aggregation in LTE-Advanced

In Long-Term Evolution-Advanced (LTE-A), which is currently in the process of standardization in the 3rd generation partnership project (3GPP), carrier aggregation (CA) was introduced as a main feature for bandwidth extension while maintaining backward compatibility with LTE Release 8 (Rel. 8). In the CA mode of operation, since two or more component carriers (CCs), each of which is compatible with LTE Rel. 8, are aggregated, mobility management for CCs such as inter/intra-frequency handover, CC addition, and CC removal is needed to provide sufficient coverage and better overall signal quality. Therefore, the signaling overhead for Radio Resource Control (RRC) reconfiguration for the mobility management of CCs in LTE-A is expected to be larger than that in LTE Rel. 8. In addition, CA allows aggregation of cells with different types of coverage, and therefore, the signaling overhead might be dependent on the coverage of each CC assumed in a CA deployment scenario. This paper presents evaluation results on the CC control overhead with several CC management policies in some CA deployment scenarios, and shows that the increase in the control overhead is not significant even in a CA deployment scenario with overlaid picocells.

Experiments on HSDPA Throughput Performance in W-CDMA Systems

In this paper, we present laboratory and field experimental results using High Speed Downlink Packet Access (HSDPA) test-beds in order to reveal the actual HSDPA performance based on key technologies such as base station (BS) scheduling, adaptive modulation and coding, hybrid automatic repeat request, and advanced receiver design. First, this paper evaluates the effects of advanced user equipment capabilities such as the maximum number of multi-codes, transmit diversity, receive diversity, and a chip equalizer. Increases in throughput of 60% and 85% due to using 10 and 15 codes were observed compared to 5 codes, respectively. The gain of 22% was obtained by applying closed-loop transmit diversity to the HSDPA network. Receive diversity improves the throughput in the region from low to high signal-to-interference ratio, and the gain of 45% was obtained by applying receive diversity to the conventional RAKE receiver. A throughput gain of approximately 17% due to the use of the chip equalizer was obtained and it was observed mainly in the high Ior/Ioc region and under multi-path conditions. Second, field experiments are conducted to elucidate the effects of multi-user diversity using a BS scheduling algorithm, and reveal that proportional fairness scheduling provides both the increase in sector throughput of 18% and a sufficient degree of fairness among users. The transmit control protocol (TCP)-level throughput performance is also investigated in order to reveal the actual end-user throughput. The results show that the throughput rate of approximately 90% of the throughput of the MAC-hs layer is achieved in the TCP layer in the laboratory experiments and in the field experiments.

Field Experiment Results of User Throughput Performance in WCDMA HSDPA

High-speed downlink packet access (HSDPA) is specified in the 3rd Generation Partnership Project (3GPP) to cope with the increasing demand for high-speed Internet-based multimedia services. This paper presents field experimental results of the user throughput performance in HSDPA to clarify the effects of the maximum number of multi-codes, transmit diversity, and advanced user equipment (UE) such as receive diversity and a chip equalizer. The field experimental results show that 15-multi-code UE, transmit diversity, and receive diversity achieve the peak throughput of 6.5, 8.5, and 10.2 Mbps, respectively, at the average moving speed of 30 km/h in an actual multi-path fading propagation channel, and the average received signal-to-interference power ratio (SIR) is 24 dB. Furthermore, the results show that transmit diversity, receive diversity, and the chip equalizer can improve the average throughput to 27.0%, 54.6%, and 12.8%, respectively, compared to the conventional single antenna Rake receiver when the average received SIR is 16.3 dB