42550314
Performance of CDPD with Timed Hop and Forced Hop
Cellular Digital Packet Data (CDPD) offers mobile users access to a low-cost, ubiquitous, wireless data network. CDPD can be overlaid on existing AMPS analog cellular systems and share their infrastructure equipment on a non-interfering basis. To prevent interference with the voice activities, CDPD performs forced hop to a channel stream when a voice request is about to use the RF channel occupied by that channel stream. In addition, several timers and system parameters are defined in CDPD to ensure that the normal AMPS activities are not affected by CDPD. This article investigates how the channel selection algorithms, the timers and other parameters affect the performance of AMPS/CDPD systems. Specifically, we study the trade-off between mean CDPD channel holding time and voice incompletion probability. Our study indicates that if AMPS exercises the most-idle channel selection algorithm and CDPD exercises the least-idle channel selection algorithm, then the largest mean CDPD channel holding time is expected. On the other hand, if AMPS exercises the least-idle channel selection algorithm, then the smallest voice incompletion probability is expected.
16744149
Performance Analysis for Dual Band PCS Networks
In a dual band personal communications services (PCS) network, heavy traffic areas are covered by microcells which overlay macrocells. In such a network, microcells and macrocells utilize different frequency bands. We propose an analytic model to study the performance of a dual band PCS architecture. Our model assumes that a PCS subscriber has a general residence time distribution in a microcell and the macrocell residence time distribution is derived from the microcell residence time distribution. An iterative algorithm is used to compute the overflow traffic from a microcell to its overlaid macrocell. Then, the call incompletion probability is computed by a macrocell model based on the overflow traffic. Our study indicates that the variance of the microcell residence time distribution and the number of microcells covered by a macrocell have significant effects on the call incompletion probability.
16848330
A flexible graphical user interface for performance modeling
We identify three goals for the graphical user interface (GUI) of a network simulation environment: user friendliness, model re-usability, and application extensibility. We address the user friendliness issue by proposing a simple yet efficient approach to setup parameters for the simulation models. We address the application extensibility issue by a two-layer GUI architecture. The two layers are loosely-coupled, and the first layer can be easily replaced (without affecting the other components of the simulation environment). We address the model re-usability issue by subnetworks. Unlike most existing simulation packages where subnetwork is simply a method to group the nodes, the subnetwork construct in our approach is an integral part of the simulation environment (i.e., all operations for a basic node also apply to a subnetwork). The port concept is used to explicitly define the I/O relationship between a subnetwork and the outside world. Parameter dialog boxes are used to set up the parameters for a subnetwork conveniently. Finally, a simple stack mechanism is proposed to measure subnetwork-wide output statistics.<<ETX>>
5110930
A comparison study of the two-tier and the single-tier personal communications services systems
A two-tier PCS system integrates the high tier PCS system and the low tier PCS systems into a single system to provide the advantages of both tiers. Such a system is expected to provide better service (more available and more cost effective to the users) at the expense of the extra tier switching management. We compare the performance of the two-tier PCS system and the single low tier system in two aspects: the registration traffic and the service availability. Because of the tier management, the two-tier system generates more registration traffic than the single low tier system. Under the range of the input parameters in our study, we show that the two-tier system generates less than 10% extra registration traffic than the single low tier system in most cases and generates less than 20% registration traffic in the worst cases. It is clear that for the service availability, the two-tier system is better than the single one tier system. We also study the probability that a call is forced terminated in the single low tier system because the low tier becomes unavailable during the call (such a call can be continued in the two-tier system).
2805042
A new random walk model for PCS networks
This paper proposes a new approach to simplify the two-dimensional random walk models capturing the movement of mobile users in personal communications services (PCS) networks. Analytical models are proposed for the new random walks. For a PCS network with hexagonal configuration, our approach reduces the states of the two-dimensional random walk from (3n/sup 2/+3n-5) to n(n+1)/2, where n is the layers of a cluster. For a mesh configuration, our approach reduces the states from (2n2-2n+1) to (n/sup 2/+2n+4)/4 if n is even and to (n/sup 2/+2n+5)/4 if n is odd. Simulation experiments are conducted to validate the analytical models. The results indicate that the errors between the analytical and simulation models are within 1%. Three applications (i.e., microcell/macrocell configuration, distance-based location update, and GPRS mobility management for data routing) are used to show how our new model can be used to investigate the performance of PCS networks.
15619003
A Graphical User Interface Design for Network Simulation
Abstract This article describes a prototyping effort of a flexible graphical user interface (GUI) for a simulation tool called COPS. The GUI is designed to allow parameter setup for all modules in simulation model, and can be easily replaced by new GUIs implemented in different languages/graphical tools. This article provides design guidelines and implementation details of the flexible GUI.
28156768
A VLSI implementation of the blowfish encryption/decryption algorithm
We propose an efficient hardware architecture for the Blowfish algorithm [1]. The speed is up to 4 bit/clock, which is 9 times faster than a Pentium. By applying operator-rescheduling method, the critical path delay is improved by 21.7%. We have successfully implemented it using Compass cell library targeted at a 0.6 μm TSMC SPTM CMOS process. The die size is 5.7x6.1 mm and the maximum frequency is 50MHz.
15077607
A transformation-based method for loop folding
We propose a transformation-based scheduling algorithm for the problem given a loop construct, a target initiation interval and a set of resource constraints, schedule the loop in a pipelined fashion such that the iteration time of executing an iteration of the loop is minimized. The iteration time is an important quality measure of a data path design because it affects both storage and control costs. Our algorithm first performs an As Soon As Possible Pipelined (ASAPp) scheduling regardless the resource constraint. It then resolves resource constraint violations by rescheduling some operations. The software system implementing the proposed algorithm, called Theda.Fold, can deal with behavioral loop descriptions that contain chained, multicycle and/or structural pipelined operations as well as those having data dependencies across iteration boundaries. Experiment on a number of benchmarks is reported. >
15551235
A hardware accelerator for context-based adaptive binary arithmetic decoding in H.264/AVC
We propose a hardware accelerator for context-based adaptive binary arithmetic decoding (CABAC) in H.264/AVC. We also propose an efficient memory system for easy integration with other components such as motion compensation and IDCT. We develop an efficient finite state machine so that our design can generate one bit every 2 to 3 clock cycles. Experimental result with FPGA prototyping shows that our design is sufficient to decode main profile CIF video streams at 30 fps.
14489226
A performance-driven standard-cell placer based on a modified force-directed algorithm
We propose a performance-driven cell placement method based on a modified force-directed approach. A pseudo net is added to link the source and sink flip-flops of every critical path to enforce their closeness. Given user-specified I/O pad locations at the chip boundaries and starting with all core cells in the chip center, we iteratively move a cell to its force-balanced location assuming all other cells are fixed. The process stops when no cell can be moved farther than a threshold distance. Next, cell rows are adjusted one at a time starting from the top and bottom. After forming these two rows (top/bottom), all movable core cells force-balanced locations are updated. The row-formation-and-update process continues until all rows are adjusted and, hence, a legal placement is obtained.
 We have integrated the proposed approach into an industrial APR flow. Experimental results on benchmark circuits up to 191K-cell (500K-gate) show that the critical path delay can be improved by as much as 11.5%. We also study the effect on both layout quality and CPU time consumption due to the amount of pseudo net added. We found that the introduction of pseudo net indeed significantly improves the layout quality.
32261160
Channel assignment for GSM half-rate and full-rate traffic
Global System for Mobile Communications (GSM) supports full-rate and half-rate calls. In this paper, we propose analytical and simulation models to study the performance of four channel assignment schemes for GSM half-rate and full-rate traffic. Our study indicates that among the four schemes, the repacking scheme has the best performance for mixing half-rate and full-rate traffic. We also observe that good performance is expected if the standard derivation of the cell residence time for a mobile station is large.