Farid Khafizov

TCP over wireless links with variable bandwidth

We analyze the effects of TCP algorithms on data transmission over links with variable bandwidth. Significant throughput degradation is demonstrated due to factors such as spurious TCP retransmissions. The degradation is shown to be severe especially when high bandwidth resources are allocated to users for time periods during which multiple TCP segments are transmitted. The throughput degradation due to TCP effects is quantified for a wide range of burst and delay durations. A model for the TCP round trip time (RTT) is developed and validated with experimental results. This model is used to provide insight into spurious TCP retransmission problem and to suggest methods to alleviate it. Consequently, various methods are proposed and evaluated to improve the system throughput. Although we focus on IS-2000 links with finite burst mode of operation, the results would apply to different systems with shared resources and slow bandwidth allocation mechanisms.

Analytical model of RLP in IS-2000 CDMA networks

Wireless data networks rely on link layer protocols to reduce relatively high frame error rates (FER) at the physical layer. One of the questions in wireless data networks design is how persistent a link-layer should be in performing retransmissions. This paper investigates this problem in the example of cdma2000 networks that employ the radio link protocol type 3 (RLP) for reducing physical layer FER. We develop an analytical model describing RLP transmission delay, residual FER and data throughput as a function of physical layer FER. We show how the model can be used to determine the dependency of TCP and RLP throughput on various RLP configuration parameters and to minimize RF cost. Model predictions are shown to agree with simulation results and were successfully applied to improving performance of a cdma2000 system.

Evaluation of performance improvement of IS-2000-A in comparison to IS-2000

IS-2000 Release 0 is the standard for the first phase of cdma2000, a 3G wireless technology. Release 0 allows a maximum single channel rate of 153.6 kb/s. The next release, IS-2000 Release A, was introduced to improve the performance of cdma2000. A key enhancement increases the maximum single channel rate to 307.2 kb/s. We evaluate the performance benefits of this higher data rate feature. Simulations show there is no significant sector throughput increase. The increase in user throughput depends on system loading, and for highly loaded systems the gain is small. We analyze the dependency of throughput gain on the system power loading, and discuss the channel rate distribution and other characteristics of system performance. We provide recommendations to maximize the benefits of the 307.2 kb/s channel and identify configurations that will not benefit from 307.2 kb/s.

QoS provisioning for voice traffic in a CDMA network

With the current developments in telecommunication industry and the shift towards highly competitive environment, delivering superb QoS is becoming increasingly important. In this paper we propose an approach to QoS provisioning for a CDMA network. The network model we consider has several parts were a considerable call loss could occur. We also address the issue of higher resource requirement due to the soft handoff. Results are illustrated with numerical examples.