System Design Issues and Performance Evaluations for Adaptive Modulation in New Wireless Access Systems

This paper discusses system design strategies and performance evaluation for adaptive modulation techniques used in new and up-and-coming wireless access systems. After a brief discussion on basic modulation parameter (MP) settings as well as functionalities specific for adaptive modulation systems, this paper discusses how to design a narrowband time-division multiple-access/time-division duplex (TDMA/TDD)-based adaptive modulation system and confirms through laboratory experiments that the narrowband TDMA/TDD-based adaptive modulation system dramatically enhances system robustness to multipath fading and flexibility in throughput and transmission quality control. Next, as an extension to many fields of application for adaptive modulation, this paper discusses subcarrier-level adaptive modulation for orthogonal frequency-division multiplexing (OFDM)-based one-cell reuse broadband cellular systems. One key result is that nonsubcarrier transmit power control (TPC) applied adaptive modulation systems can achieve almost the same performance as subcarrier TPC applied adaptive modulation systems provided that the required signal-to-noise-plus-interference power ratio increment in the MP sets is designed to be sufficiently small. Finally, this paper explains the dynamic parameter controlled OFDM/TDMA system as an example of a practical scheme for one-cell reuse broadband wireless access systems. The analysis confirms that this adaptive system can achieve a spatial reuse efficiency defined by (average throughput in multicell conditions)/(average throughput in single cell conditions) of 0.8 as well as an average media access control payload throughput of about 150 Mb/s using about 100 MHz of bandwidth.