Gustav Wikström

LTE release 14 outlook

Todays 4G LTE systems bring unprecedented mobile broadband performance to over a billion of users across the globe. Recently, work on a 5G mobile communication system has begun, and next to a new 5G air interface, LTE will be an essential component. The evolution of LTE will therefore strive to meet 5G requirements and to address 5G use cases. In this article, we provide an overview of foreseen key technology areas and components for LTE Release 14, including latency reductions, enhancements for machine-type communication, operation in unlicensed spectrum, massive multi-antenna systems, broadcasting, positioning, and support for intelligent transportation systems.

Uplink PHY Design with Shortened TTI for Latency Reduction

Shortening the transmit time interval (TTI) has been considered in 3GPP LTE as an effective way for latency reduction. In this paper, we discuss the physical layer design aspects for uplink data transmissions with short TTI (sTTI). Here, an sTTI consists of one or a few SC-FDMA symbols, and its time duration is less than 1 ms. Different methods of demodulation reference signals (DMRS) design, DMRS sharing and DMRS multiplexing, are introduced to reduce the reference signal overhead when shortening the TTI length. Our link level simulation results show that both methods can efficiently reduce the DMRS overhead, and thereby improve the system throughput. Moreover, we show that due to better channel estimates, a shorter TTI, e.g., 2-symbol TTI, is more robust towards high Doppler scenarios. In contrast, for a 7-symbol TTI, which is 0.5 ms, more than one reference symbols can be inserted in order to improve the channel estimates in high Doppler scenarios. Finally, a discussion is given on how several short TTIs can be multiplexed into the frame format used for LTE.

Analysis of the potential for increased spectral reuse in wireless LAN

By allowing simultaneous transmissions in neighbouring cells the spectral reuse and the overall throughput of a WLAN system can be increased. We have investigated the impact of varying the clear channel assessment threshold (CCAT) in different network deployments defined by IEEE 802.11ax Task Group, and we show the potential of 4 different algorithms. By increasing the CCAT value from todays legacy value of -82 dBm to -62 dBm, an increase of up to 23% in the mean user throughput is observed. Further improvements are observed by using more advanced algorithms such as dynamic sensitivity control (DSC). The performance is also compared to those of reuse 1 systems and systems with uplink-downlink separation.