科研成果详情

This report presents an empirical study on the performance of mobile High Speed Packet Access (HSPA, a 3G+ cellular standard) networks in Hong Kong via extensive field tests. Our tests, from the viewpoint of end users, cover virtually all possible mobile scenarios in urban areas, including subways, trains, off-shore ferries and city buses. Our field measurement results show new findings on the performance of mobile HSPA networks, which greatly differ from that of static HSPA networks, namely, (i) mobility significantly degrades HSPA performance, but HSPA on subways show the least performance degradation compared with other mobile scenarios, (ii) the largest impact on the mobile HSPA performance comes from handoffs and ping-pong effects, which are long thought to have been properly handled since the time of 2G networks, (iii) there exists a high degree of link asymmetry in which uplink deteriorate than downlink in mobility, (iv) mobility improves fairness of bandwidth sharing among users, (v) operators manipulate connection policies to maximize their benefits and affect user experience, but mobility reduces the probability that these policies take effect. The test results indicate that current HSPA networks are not ready to support real-time applications in mobile environments with heavy multimedia traffic such as video communications, unless substantial improvements are made to stabilize link qualities. The test results are useful to network planners for improving cell coverage to provide subscribers with better quality of service, and to application developers for designing flow control algorithms to overcome bandwidth variability when subscribers are mobile.