A transmission convergence sublayer for wireless ATM with code division multiple access (CDMA)

Abstract

Asynchronous transfer mode (ATM) is rapidly emerging as a key transport mechanism of future multimedia networks, and wireless networks are being widely deployed to provide personal communication services. Thus future ATM networks are expected to comprise wireline as well as wireless subnetworks and the interoperability of wireless and wireline ATM networks becomes increasingly important. To facilitate interoperability of wireless and wireline subnets, it is desirable to retain the standard ATM cell as a universal basic unit of information transfer across all subnets. The paper specifies a transmission convergence (TC) sublayer that protects ATM cells against clustered errors and supports standard ATM on wireless media with a CDMA scheme. It proposes a forward error correction scheme for inclusion in the TC sublayer and investigates its performance for different spread spectrum schemes. The results of this study indicate the following. Without a forward error correction mechanism at the TC sublayer almost all ATM cells on a wireless ATM channel are corrupted, and the throughput of the wireless ATM link is almost zero. A 5-7 byte error correction function at the TC sublayer is required to provide an acceptable cell error ratio on a wireless ATM channel. Hence, each TC protocol data unit (TC-PDU) of the proposed TC sublayer consists of a standard 53 byte ATM cell and a 10-14 bytes long cell protection field (CPF). With a bandwidth expansion factor of 128, and supporting approximately 8 users, a code division multiple access (CDMA) scheme for PCS-type microcellular applications could support a CER of 10/sup -7/ or less, with a 10-14 bytes long CPF, and a SNR of approximately 12 dB.