Dennis Ray Schaeffer

Voice over IP (VOIP) over cellular: HRPD-A and HSDPA/HSUPA

Third generation wireless communication systems, such as High Rate Packet Data (HRPD-A), also known as 1xEV-DO Revision A, and High Speed Downlink/Uplink Packet Access (HSDPA/HSUPA) have been standardized to support high-speed data and Internet access in cellular systems. Advanced techniques such as adaptive modulation and coding, Hybrid ARQ (H-ARQ), fast scheduling and a de- centralized architecture have been included in these systems to achieve high peak data rate and significantly higher sector and user throughput. It is shown that approximately 35-40 Erlangs could be supported with a delay bound of around 250 msec for mobile-to-mobile call for HRPD-A and around 90- 100 Erlangs for HSDPA/HSUPA combination with a similar delay bound of HRPD-A.

Efficient Monte-Carlo simulation of a product-form model for a cellular system with dynamic resource sharing

There are many ways for users to share the radio spectrum allocated to a cell in a cellular phone system. We analyze a commonly proposed scheme wh ere the cell is divided into s sectors. Each sector has exclusive access to a certain number of channels. The remaining channels reside in a “common pool” and are shared among the sectors. The smallest unit of bandwidth that can be borrowed from the common pool is a “carrier,” which consists of c channels. When viewed as a multidimensional birth-death process, the steady-state distribution of the number of active channels in each sector has a “product form,” but because the state space is large and has a nonlinear boundary, direct calculation of quantities of interest is usually impractical. Ross and Wang have developed a Monte-Carlo technique that applies to our problem. We significantly improve the efficiency of their technique when applied to our problem by including certain (nonlinear) control variates. The kinds of control variates we use can be applied to other loss systems as well. We also explore the effect of importance sampling for our system. In many cases the variance reduction achieved from the combination of importance sampling and control variates is far greater than from either method alone. For systems with blocking probabilities in the range 0.001 to 0.1, the variance of the system-blocking probability estimator can be reduced by several orders of magnitude.

HRPD-A downlink voice/IP and data throughput and delay analysis

HRPD-A adds new forward and reverse link rates and a forward link multi-user packet capability at the MAC layer. Completed simulations reveal the performance characteristics of this system in the 1.9 GHz frequency band. These characteristics consist of capacities of voice/IP traffic and mixed data and voice/IP traffic. Downlink data traffic models consist of FTP, HTTP (Web browsing), WAP, and video streaming models. The simulation assumptions include the ITU channel models and 3GPP2 data traffic models