SEAMLESS HANDOVER AT HIGH SPEEDS FOR CELLULAR RANGE TELEMETRY

Abstract

Cellular based Range Telemetry provides a lot of benefits over legacy Aeronautical Mobile Telemetry, such as: • Higher capacity, allowing multiple test articles (i.e. telemetry radio links) which have active telemetry data measurements exchanged in near real time. • Bi-directional radio links, that can allow new signaling with the avionics equipment on the test articles. • Higher performance provided by spectrally efficient OFDMA waveform used in LTE and the dynamic link adaptation that is built into the LTE waveform. With the CRTM cellular approach, the overall range coverage area is broken into multiple coverage areas, each served by a single cell. To maintain seamless service throughout the test flight, CRTM must support seamless mobility as the aircraft moves between the coverage areas of these cells. This is achieved using the connected mode handover procedures supported by LTE technology. Traditional LTE networks rely on signal strength measurements made by the User Equipment (UE) to make handover decisions. The measurement system and handover procedures have been designed to support mobility at speeds under 500 km/hr. To support mobility at higher speeds, the following need to be taken into account: - LTE User Equipment (UE) RF Signal Measurements: Accuracy of measurements depends on UE’s capability to measure the signal strength of a neighbor cell while synchronized to its serving cell. The higher Doppler shifts expected in an AMT environment due to the higher test article speeds and the higher frequency of operation along with the difference in Doppler shifts between the serving cell and neighbor cells complicates cell measurements. - Handover Processing Time: The serving eNodeB needs to process the measurements from the UE and initiate handover in a timely manner. Delays in handover processing can result in radio link failures. The higher speeds of test articles in the AMT environment reduces the time available to the eNodeB for handover processing. This paper explains the handover procedure in 4G LTE, with the focus on: Measurement reports that support handover decisions Decisions impacting data service delays during handover impacts to the handover processing when the UE (i.e. test article in CRTM) is moving at very high speed.