  As a key pillar technology for the future 6G networks, terahertz (THz)
communication can provide high-capacity transmissions, but suffers from severe
propagation loss and line-of-sight (LoS) blockage that limits the network
coverage. Narrow beams are required to compensate for the loss, but they in
turn bring in beam misalignment challenge that degrades the THz network
performance. The high sensing accuracy of THz signals enables integrated
sensing and communication (ISAC) technology to assist the LoS blockage and user
mobility-induced beam misalignment, enhancing THz network coverage. In line
with the 5G beam management, we propose a joint synchronization signal block
(SSB) and reference signal (RS)-based sensing (JSRS) scheme to predict the need
for beam switches, and thus prevent beam misalignment. We further design an
optimal sensing signal pattern that minimizes beam misalignment with fixed
sensing resources, which reveals design insights into the time-to-frequency
allocation. We derive expressions for the coverage probability and spatial
throughput, which provide instructions on the ISAC-THz network deployment and
further enable evaluations for the sensing benefit in THz networks. Numerical
results show that the JSRS scheme is effective and highly compatible with the
5G air interface. Averaged in tested urban use cases, JSRS achieves near-ideal
performance and reduces around 80% of beam misalignment, and enhances the
coverage probability by about 75%, compared to the network with 5G-required
positioning ability.
