Interference aware throughput measurements for mobile WiMAX over vehicular radio channels

Due to its advantageous properties in multipath propagation scenarios, the Orthogonal Frequency Division Multiple Access (OFDMA) radio transmission scheme is widely spread in current broadband wireless networks. Exemplary emerging systems based on this technology are the UMTS Long Term Evolution (LTE), Mobile WiMAX and some popular WiFi variants (e.g. IEEE 802.11n). Although analytical and simulative investigations have shown that the increased symbol time of OFDMA (compared with single carrier systems) allows for a wider delay spread without causing Inter Symbol Interference (ISI) it is quite hard to quantify this improvement under realistic circumstances. In this paper, we present the results of a measurement campaign in which we investigated the influence of multipath fading channels, interferences and velocity on the available User Datagram Protocol (UDP) data rate of an IEEE 802.16e conform Mobile WiMAX System. Therefore, a sophisticated laboratory setup was used which is based on a radio channel emulator. From that, optimum switching points for the Adaptive Modulation and Coding (AMC) scheme are derived. The results show, that for vehicular radio channels the choice of the most suitable modulation and coding scheme, and therefore the maximum available data rate, does strongly depend on the environmental parameter such as delay spread and user velocity. In particular, it can be seen that the use of a strong forward error correction is more important than a higher order modulation scheme if high data rates are required by real time multimedia applications.