  The exponential rise in mobile traffic originating from mobile devices
highlights the need for making mobility management in future networks even more
efficient and seamless than ever before. Ultra-Dense Cellular Network vision
consisting of cells of varying sizes with conventional and mmWave bands is
being perceived as the panacea for the eminent capacity crunch. However,
mobility challenges in an ultra-dense heterogeneous network with motley of high
frequency and mmWave band cells will be unprecedented due to plurality of
handover instances, and the resulting signaling overhead and data interruptions
for miscellany of devices. Similarly, issues like user tracking and cell
discovery for mmWave with narrow beams need to be addressed before the
ambitious gains of emerging mobile networks can be realized. Mobility
challenges are further highlighted when considering the 5G deliverables of
multi-Gbps wireless connectivity, <1ms latency and support for devices moving
at maximum speed of 500km/h, to name a few. Despite its significance, few
mobility surveys exist with the majority focused on adhoc networks. This paper
is the first to provide a comprehensive survey on the panorama of mobility
challenges in the emerging ultra-dense mobile networks. We not only present a
detailed tutorial on 5G mobility approaches and highlight key mobility risks of
legacy networks, but also review key findings from recent studies and highlight
the technical challenges and potential opportunities related to mobility from
the perspective of emerging ultra-dense cellular networks.

Networking and Internet Architecture;Artificial Intelligence