Two-way TCP performance issues and solutions in asymmetric LTE radio access

Due to the joint evolution of mobile applications and cloud services, mobile users routinely act as both content consumers and producers. Nowadays there is an increasing trend in both the downlink (DL) and uplink (UL) data traffic, which are predominantly Transmission Control Protocol (TCP) based. Simultaneous DL and UL TCP transmission over an asymmetric link causes significant throughput degradation in the direction with higher capacity whenever TCP data and acknowledgment (ACK) segments are not treated separately. The radio access links of the Long Term Evolution (LTE) systems are asymmetric with higher capacity in the DL than in UL, making LTE prone to the asymmetry problem. In this context, the degradation is caused by multiplexing data and ACKs in the same User Equipment (UE) buffer before UL transmission. This paper proposes and evaluates three novel alternatives that solve the problem at the network side, i.e., transparently to the end devices. Simulation results indicate that the solutions can efficiently detect and resolve the asymmetry problem and they are able to reach the theoretical optimum within 1-5%. Excellent performance is provided even in the presence of complex web traffic.