Internet Access Performance in LTE TDD

The Time Division Duplex (TDD) uplink-downlink configuration of the 3GPP Long Term Evolution (LTE) determines how the ten subframes in a radio frame are divided between the downlink and the uplink. The specified configurations cover a wide range of allocations from a downlink-heavy resource distribution ratio (9:1) to an uplink-heavy ratio (2:3). In this paper, we compare the performance of Internet access using the TCP protocol in different downlink-heavy asymmetries. We find that the performance depends on many factors such as the transferred file size, the control channel errors and the downlink/uplink traffic mix. When the file size is small, TDD can not fully utilize its potentially higher downlink capacity because of longer uplink access delays as well as shortage of uplink resources in the chosen configurations. With an increased file size, this effect fades away and TDD provides higher download bit rates than FDD. The realized increase in bit rate is however not as high as the calculated increase in available downlink resources.