Taejoon Kim

Cache-oblivious ray reordering

We present a cache-oblivious ray reordering method for ray tracing. Many global illumination methods such as path tracing and photon mapping use ray tracing and generate lots of rays to simulate various realistic visual effects. However, these rays tend to be very incoherent and show lower cache utilizations during ray tracing of models. In order to address this problem and improve the ray coherence, we propose a novel Hit Point Heuristic (HPH) to compute a coherent ordering of rays. The HPH uses the hit points between rays and the scene as a ray reordering measure. We reorder rays by using a space-filling curve based on their hit points. Since a hit point of a ray is available only after performing the ray intersection test with the scene, we compute an approximate hit point for the ray by performing an intersection test between the ray and simplified representations of the original models. Our method is a highly modular approach, since our reordering method is decoupled from other components of common ray tracing systems. We apply our method to photon mapping and path tracing and achieve more than an order of magnitude performance improvement for massive models that cannot fit into main memory, compared to rendering without reordering rays. Also, our method shows a performance improvement even for ray tracing small models that can fit into main memory. This performance improvement for small and massive models is caused by reducing cache misses occurring between different memory levels including the L1/L2 caches, main memory, and disk. This result demonstrates the cache-oblivious nature of our method, which works for various kinds of cache parameters. Because of the cache-obliviousness and the high modularity, our method can be widely applied to many existing ray tracing systems and show performance improvements with various models and machines that have different cache parameters.

RACBVHs: Random-Accessible Compressed Bounding Volume Hierarchies

We present a novel compressed bounding volume hierarchy (BVH) representation, random-accessible compressed bounding volume hierarchies (RACBVHs), for various applications requiring random access on BVHs of massive models. Our RACBVH representation is compact and transparently supports random access on the compressed BVHs without decompressing the whole BVH. To support random access on our compressed BVHs, we decompose a BVH into a set of clusters. Each cluster contains consecutive bounding volume (BV) nodes in the original layout of the BVH. Also, each cluster is compressed separately from other clusters and serves as an access point to the RACBVH representation. We provide the general BVH access API to transparently access our RACBVH representation. At runtime, our decompression framework is guaranteed to provide correct BV nodes without decompressing the whole BVH. Also, our method is extended to support parallel random access that can utilize the multicore CPU architecture. Our method can achieve up to a 12:1 compression ratio, and more importantly, can decompress 4.2 M BV nodes ({=}135 {\rm MB}) per second by using a single CPU-core. To highlight the benefits of our approach, we apply our method to two different applications: ray tracing and collision detection. We can improve the runtime performance by more than a factor of 4 as compared to using the uncompressed original data. This improvement is a result of the fast decompression performance and reduced data access time by selectively fetching and decompressing small regions of the compressed BVHs requested by applications.

Throughput analysis considering coupling effect in ieee 802.11 networks with hidden stations

This letter investigates the throughput performance of the IEEE 802.11 networks with hidden stations. Note that the decoupling approximation of the Bianchis Markov chain model is valid for the IEEE 802.11 networks with a large number of the hidden stations. Hence, we propose a new analytic model to accommodate the effect of the hidden stations and estimate the network throughput based on the analytic model.

Quality of service supporting downlink scheduling scheme in worldwide interoperability for microwave access wireless access systems

IEEE 802.16 is a standardisation for a broadband wireless access in metropolitan area networks (MAN). Since the IEEE 802.16 standard defines the concrete quality of service (QoS) requirement, a scheduling scheme is necessary to achieve the QoS requirement. Many scheduling schemes are proposed with the purpose of throughput optimisation and fairness enhancement, however, few scheduling schemes support the delay requirement. In this study, the authors propose a new scheduling scheme reflecting the delay requirement. Specifically, the authors add the delay requirement term in the proportional fair scheduling scheme and the scheduling parameters are optimised with respect to the QoS requirement. Therefore the QoS requirement is achieved without the excessive resource consumption.

Capacity and fairness tradeoff in multiuser scheduling system with reduced feedback

Multiuser diversity is an effective technique to increase the capacity of wireless networks. However, the poor fairness among the mobile stations (MSs) and the heavy feedback load as the number of MSs increases are the main problems in implementing multiuser diversity. We propose a new scheduling scheme with opportunistic feedback. Specifically, the schedule for multiple users is based on two different criteria such as the absolute SNR and the normalized SNR. Simulation result shows that the tradeoff between capacity and fairness can be fine-tuned through the proposed scheduling scheme.

T-ReX: Interactive Global Illumination of Massive Models on Heterogeneous Computing Resources

We propose several interactive global illumination techniques for a diverse set of massive models. We integrate these techniques within a progressive rendering framework that aims to achieve both a high rendering throughput and an interactive responsiveness. To achieve a high rendering throughput, we utilize heterogeneous computing resources consisting of CPU and GPU. To reduce expensive data transmission costs between CPU and GPU, we propose to use separate, decoupled data representations dedicated for each CPU and GPU. Our representations consist of geometric and volumetric parts, provide different levels of resolutions, and support progressive global illumination for massive models. We also propose a novel, augmented volumetric representation that provides additional geometric resolutions within our volumetric representation. In addition, we employ tile-based rendering and propose a tile ordering technique considering visual perception. We have tested our approach with a diverse set of large-scale models including CAD, scanned, simulation models that consist of more than 300 million triangles. By using our methods, we are able to achieve ray processing performances of 3 M~20 M rays per second, while limiting response time to users within 15~67 ms. We also allow dynamic modifications of light, and interactive setting of materials, while efficiently supporting novel view rendering.

HCCMeshes: Hierarchical-Culling oriented Compact Meshes

Hierarchical culling is a key acceleration technique used to efficiently handle massive models for ray tracing, collision detection, etc. To support such hierarchical culling, bounding volume hierarchies (BVHs) combined with meshes are widely used. However, BVHs may require a very large amount of memory space, which can negate the benefits of using BVHs. To address this problem, we present a novel hierarchical‐culling oriented compact mesh representation, HCCMesh, which tightly integrates a mesh and a BVH together. As an in‐core representation of the HCCMesh, we propose an i‐HCCMesh representation that provides an efficient random hierarchical traversal and high culling efficiency with a small runtime decompression overhead. To further reduce the storage requirement, the in‐core representation is compressed to our out‐of‐core representation, o‐HCCMesh, by using a simple dictionary‐based compression method. At runtime, o‐HCCMeshes are fetched from an external drive and decompressed to the i‐HCCMeshes stored in main memory. The i‐HCCMesh and o‐HCCMesh show 3.6:1 and 10.4:1 compression ratios on average, compared to a naively compressed (e.g., quantized) mesh and BVH representation. We test the HCCMesh representations with ray tracing, collision detection, photon mapping, and non‐photorealistic rendering. Because of the reduced data access time, a smaller working set size, and a low runtime decompression overhead, we can handle models ten times larger in commodity hardware without the expensive disk I/O thrashing. When we avoid the disk I/O thrashing using our representation, we can improve the runtime performances by up to two orders of magnitude over using a naively compressed representation.

Queuing Analysis in a Multiuser Diversity System With Adaptive Modulation and Coding Scheme

In wireless packet networks, the performance of multiuser diversity schedulers has been analyzed with the saturation assumption; however, the finite queue length effect should be taken into account. We propose a new scheduling scheme exploiting multiuser diversity that considers not only channel information but queue information as well. Considering the finite queue length effect and adaptive modulation and coding scheme (AMCS), we analyze the performance of the proposed scheduler.

RACBVHs: random-accessible compressed bounding volume hierarchies

Bounding volume hierarchies (BVHs) are widely used to accelerate the performance of various geometric and graphics applications. These applications include ray tracing, collision detection, visibility queries, dynamic simulation, and motion planning. These applications typically precompute BVHs of input models and traverse the BVHs at runtime in order to perform intersection or culling tests.

HCCMeshes: hierarchical-culling oriented compact meshes

Ray tracing and collision detection are widely used for providing high-quality visualizations and user interactions. In these algorithms, we need to detect intersecting primitives between two input objects (e.g., a ray and a 3D object in ray tracing and two 3D objects in collision detection). In order to efficiently detect these intersecting primitives, hierarchical traversal and culling by using bounding volume hierarchies (BVHs) are commonly used.