Service and system enhancements for TDMA digital cellular systems

摘要

Throughout 1998, the TDMA community investigated and defined an enhanced suite of voice and data services for TIA/EIA-136 while also improving its basic system capabilities. These enhancements, collectively named 136+, provide improved voice quality, increased capacity, higher data rates, and improved tools for RF system engineering. The enhancements are obtained by introducing a new modulation scheme (8-PSK), new slot formats, and the addition of several new interleaving and coding options. As a result, TIA/EIA-136 now supports a new vocoder mode, the GSM enhanced full-rate (US1) for improved fidelity applications, a robust IS-641 vocoder mode with a 4 dB BER enhancement on the IS-136 downlink, and a new packet data service capable of providing usable data rates of 14.4, 28.8, or 43.2 kb/s on a full-rate, double full-rate, or triple full-rate channel, respectively. The packet data service is truly evolutionary in nature, having a new medium access control layer with a network layer very similar to that used for the existing digital control channel. In addition, it maximizes commonalities among TDMA technologies, using identical higher layers and network architecture to the general packet radio service specified in GSM. Furthermore, by using a concept known as tunneling to pass TIA/EIA-136 messages through the GPRS network elements, the existing features defined on the DCCH are maintained. This article provides an overview of these 136+ applications, as well as insight into near-term improvements, such as the ability to support six voice users per 30 kHz (IDMA6), downlink time diversity, and fast power control.