Spectral Efficiency of Time Division Duplex Fixed Wireless Cellular System for Dynamic Traffic

We analyze 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. In this paper, we investigate how asymmetric and dynamic traffic affects spectral efficiency of TDD systems. Recently, dynamic TDD (D-TDD) has gained much attention as an efficient duplex scheme for high-speed data communications, because adaptive switching ability enables system to obtain statistical multiplexing gain by exploiting dynamic and asymmetric data traffic. However, it has been noted that co-channel interference can be present due to adaptive switching in a cellular network that uses frequency reuse. Thus, benefits of dynamic TDD may not be justifiable, unless a proper countermeasure is employed. To suppress the effect of strong co-channel interference, we employ time slot allocation (TSA) strategy along with sector antenna layout, as proposed in our previous work [1]. We note that 9 times higher spectral efficiency is obtained in D-TDD systems by employing TSA strategy. We also evaluate spectral efficiency of D-TDD system employing adaptive modulation, assuming traffic is delay tolerant. It is observed that 26 times higher spectral efficiency can be obtained by employing adaptive modulation. The effect of frame loading condition is also evaluated. Our computer simulation results show that spectral efficiency of D-TDD system with time slot allocation algorithm is more than that of static TDD (S-TDD) over a wide range of frame loading conditions. As a conclusion, when TSA algorithm is employed in D-TDD system employing conventional fixed modulation scheme, statistical multiplexing gain can be obtained for a fairly wide range of frame loading, compared to a S-TDD system.