Techniques for Enabling Low Latency Operation in LTE Networks

This paper describes the physical (PHY) layer and medium access control (MAC) layer design updates for Long Term Evolution (LTE) air interface that enable low latency services in LTE cellular networks. In both downlink and uplink, the low latency communication is enabled through the reduction of the transmission time interval (TTI). Reducing the TTI can be viewed as the key enabler for mission critical applications, where system capacity is not of primary importance. This paper, however, shows that enabling low latency operation in LTE networks does not have to come at the expense of capacity. Indeed, we show that the low latency operation can even increase system capacity. In particular, the TTI reduction enables shorter channel state information (CSI) and hybrid automatic repeat request (HARQ) feedback timelines, thereby leading to a more accurate rate control. Hence, a more efficient use of air interface resources becomes possible. This, in turn, translates into a higher perceived user throughput and higher system capacity. In the uplink, TTI reduction leads to a faster user scheduling and a faster access to the medium. Further, it reduces the delay in sending transmission control protocol (TCP) acknowledgments. The benefits are more pronounced during the slow start phase as the reduction in the timeline to access the medium directly translates to a faster download of data.