Studies on Data Transport Protocols for Wireless Cellular Networks

Mobile Internet technology based on wireless cellular networks has been rapidly deployed over the last several years. In the Internet, TCP (Transmission Control Protocol) is used as a standard transport layer protocol. TCP was developed in the early 1970s and has been continuously improved. Though it was designed for a wired network, it has also been used for wireless networks but without enough study or evaluation. Digital mobile phone services based on wireless cellular networks, such as PDC (Personal Digital Cellular) or GSM (Global System for Mobile communications), were first provided in the early 1990s. These services will be further developed based on high-speed packet data transmission as IMT-2000 (International Mobile Telecommunications 2000) services in the early 2000s. In this thesis, we study TCP as a data transport protocol for wireless cellular networks based on the IMT-2000 system. In studying the use of TCP over wireless cellular networks, certain issues need to be considered. First, we should consider the characteristics of the underlying data link protocol. Secondly, packet losses due to transmission errors on the wireless link cause unexpected degradation of TCP throughput. In this thesis, we first evaluate TCP performance by explicitly mod-eling the performance characteristics of the underlying data link layer protocol. We adopt slotted ALOHA, a multiple access method, as the data link layer protocol. Then, we construct an analytical model for TCP throughput in the wireless cellular that takes into consideration the influence of slotted ALOHA. Using our method, we next evaluate TCP throughput through the wireless cellular network and show that improving throughput at the data link layer level does not necessarily lead to improved TCP throughput. We also show that the greater reliability provided by data transmission enhancement in the lower layer protocols, such as ARQ (Automatic Repeat reQuest) and FEC (Forward Error Correction), can improve TCP performance. It is especially important for error correction to adequately change the ii FEC parameters according to the noise level. Next, we study the problem of packet losses due to transmission errors causing unexpected degradation of TCP throughput in a wireless cellular network. Many approaches to improving TCP throughput in a wireless cellular network have been reported. We summarize these approaches and evaluate TCP performance, through which we find the appropriate FEC code for a given BER (Bit Error Rate). Based on above these results, we propose a new adaptive FEC scheme that combines these approaches, and …