The Impact of Interference on an OFDM System with AMC, Hybrid ARQ, and a Finite Queue on End-to- End Performance

Abstract — Several technologies have been added to wireless communication systems that increase reliability of these systems and afford them higher data rates. These new technologies when combined with the multiple layers of a communications network make the analysis of these systems increasingly complex. The work here analyzes the impact of placing a modulated interfering transmission in the guard band of a wireless packet based (infrastructure) network on the end user TCP performance. Wireless networks, such as LTE, employ at the physical layer orthogonal frequency division multiplexing (OFDM) and adaptive modulation and coding (AMC) while at the data-link layer they use hybrid auto-repeat-request (HARQ) and a finite length queue; they also utilize cross-layer optimization to improve performance. These protocols allow the wireless network the ability to adapt to an ever changing fading environment. The following work shows the effect of a modulated interfering signal in the guard band of an OFDM system on the end-to-end TCP performance. In some cases the impact from the interference is indistinguishable from the effects of channel fading. Keywords—Transport protocol (TCP); Interference; Orthogonal frequency division multiplexing (OFDM); Fading