  A non-terrestrial network (NTN), a term coined by the 3rd Generation
Partnership Project (3GPP), refers to a network utilizing airborne or
spaceborne payload for communication. The use of NTN has the potential of
facilitating providing connectivity to underserved areas. This has motivated
the work in 3GPP on evolving the fifth generation (5G) wireless access
technology, known as new radio (NR), to support NTN. The broadband
opportunities promised by NTN with low Earth orbit (LEO) satellites have
attracted much attention, but the performance of LEO NTN using 5G NR has not
been well studied. In this paper, we address this gap by analyzing and
evaluating the throughput and capacity performance of LEO NTN. The evaluation
results show that the downlink capacity of a LEO satellite in S band with 30
MHz bandwidth serving handheld terminal is about 600 Mbps and the downlink
capacity of a LEO satellite in Ka band with 400 MHz bandwidth serving very
small aperture terminal (VSAT) is about 7 Gbps. For a LEO NTN similar to the
Kuiper project proposed by Amazon, we find that, due to the large cell sizes in
the LEO NTN, the area capacity density is moderate: 1-10 kbps/km$^2$ in the S
band downlink and 14-120 kbps/km$^2$ in the Ka band downlink depending on
latitude.
