Recently, we have received a growing number of reports that complain about poor and unstable internet connections at bus stops in metro Seoul. Careful analyses led us to conclude that Wi-Fi APs equipped on buses instigate the trouble. According to the ambitious free Wi-Fi expansion plan by the city of Seoul, public buses started to equip Wi-Fi APs. As buses with APs stop and go, they actualize intermittent connection opportunities to riders waiting at the bus stops. However, the connection durations are too short such that bus APs are a nuisance rather than a convenience. We collected the basic statistics such as AP inter-arrival and sojourn times and measured link level performance metrics. We observed the effect of frequent frame losses on the TCP congestion control and eventually on the TCP throughput. We also measured the performance of applications such as PLT (Page Load Time). The measurement results showed that passing APs are useful only for some applications in very limited situations while they are virtually useless and just irritations in many cases. We also discovered that poor Wi-Fi connections pervert MPTCP; MPTCP performs worse than the generic single path TCP over the LTE network. We expect that our results will be used as the reference data in redesigning Wi-Fi offloading mechanisms as well as in planning and deploying urban Wi-Fi networks.

Novel approaches to parallel H.264 decoder for symmetric multicore processors are presented. The basic partitioning of the decoder is coarse-grained and hybrid method of the data partitioning and functional partitioning. We investigate the performance bottleneck of the parallelized decoder, and propose two new approaches, software memory throttling and fair load balancing. The software memory throttling limits the number of cores involved in the parallel motion compensation to achieve better speedup and power-saving. The fair load balancing for deblocking filter reduces load imbalance caused by the conventional static partitioning method. From the evaluation on two different symmetric multicore platforms, proposed approaches show up to 24% of speedup when there is much bandwidth contention.

We propose a new method for H.264/AVC parallel decoder implementation on the CELL Broadband Engine processor. To decode the full HD H.264 stream in real time, the high performance processing is required due to the high computation and complexity. Our decoder exploits the functional partition method to parallelize the H.264 decoder on multicore platform. The load of performance critical module is dynamically balanced with less computational module to fully utilize of the multicore processors. The experimental results of proposed load balancing method show that it runs about 1.4 times faster than the normal parallel decoder with same hardware requirement - 1 PPE and 3 SPEs. This result is more than 4 times faster performance than that of the single core decoder - PPE only.