Spectral efficiency of time division duplex fixed wireless cellular system for dynamic traffic

Abstract

We analyze the spectral efficiency of a dynamic time division duplex system in a fixed wireless cellular network. Conventionally, spectral efficiency has been analyzed under static and fully-loaded conditions. We investigate how asymmetric and dynamic traffic affects TDD system spectral efficiency. Dynamic TDD (D-TDD) is an efficient duplex scheme for high-speed data communications; it exploits dynamic and asymmetric data traffic. However, cochannel interference can be present, so the benefits of dynamic TDD may not be justifiable, unless a proper countermeasure is employed. To suppress the effects of strong cochannel interference, we employ a time slot allocation (TSA) strategy along with a sector antenna layout (Jeong, W.-C. and Kavehrad, M., IEEE Trans. Commun., vol.50, no.10, p.1627-36, 2002). By employing the TSA strategy, 9 times higher spectral efficiency is obtained in D-TDD systems. We also evaluate the spectral efficiency of a D-TDD system employing adaptive modulation, assuming traffic is delay tolerant. By employing adaptive modulation, 26 times higher spectral efficiency can be obtained. The effect of frame loading condition is also evaluated. When the TSA algorithm is employed in a D-TDD system employing a conventional fixed modulation scheme, statistical multiplexing gain can be obtained for a fairly wide range of frame loading, compared to a static TDD system.