# User Association Performance Trade-Offs in Integrated RF/mmWave/THz Communications
## 6 Results
If a link is not blocked, then the path loss exponent is set to\(PL_{LOS}\), and the received signal and interference are calculated normally based on the distance, fading gains, and antenna gains. THz wireless communication system is modeled using molecular absorption loss and exponential path loss. Also, system losses (L) are defined. The total noise consists of thermal noise and molecular noise. This simulation models a wireless network with multiple base stations supporting different frequency bands, including RF, mmW and THz. Users are distributed in the network area and can associate with different base stations based on the radio link quality and blockage risk. Environmental factors like propagation loss, blockage from walls, buildings, etc., are modeled to realistically capture how the signal strength (SINR) and link blockage probability vary across frequency bands and locations. The algorithm periodically evaluates SINR and blockage models to compute the association scores for each user-BS pair. It then reassociates users in batches to balance loads while considering each user's data needs and preferred band based on their category (e.g., high data and low latency). Network metrics like throughput and satisfaction levels are monitored over time as environmental conditions and user profiles dynamically change. This provides an end-to-end simulation of the multi-band user association approach to validate its effectiveness under realistic radio channel and deployment scenarios. The methodology considers changes to the network topology and BSs deployments over the simulated time period. The environment and network configuration are not static--they evolve dynamically as part of the long-term simulation. The algorithm periodically re-evaluates user associations and network metrics, as both the environmental/user conditions and underlying network topology/deployments change and adapt over time. As an example to clarify the UE profile change, UE profiles change with respect to latency/reliability requirements during the simulation. Each user is classified/categorized based on their expected data usage and priority needs. For example, some users may be considered \"low latency critical\" like VoLTE, while others are \"high data\" like video streaming. These categories define the user's preferred network characteristics--i.e., low-latency users want fast response times above all. However, a user's real-time needs are not static--a video caller may sometimes prioritize latency over reliability. To model this, each user's profile is associated with a time-varying probability distribution. For instance, a user has an 80 percent chance of being \"low latency\" but 20 percent of being \"high reliability\" at any given instant. When user profiles are updated, these probabilities are sampled to randomly switch users between categories. This simulates how priorities may change--a gaming user may occasionally download large files. The algorithm then adapts user associations accordingly to meet altered performance demands, capturing a more realistic scenario than that based on fixed assumptions about each user. Figure 2 shows a comparison of load distribution for the proposed user association algorithm with max-SINR. For RF bands (sub-6 GHz), the number of users could range from a few hundred to over 1000 users within a 2000 m \(\times\) 2000 m area depending on traffic levels. The number of base stations of usually 1-4 BSs would be needed to provide coverage within this area. For mmW bands (24-100 GHz), due to higher path loss, smaller cell sizes are needed (100 s of meters). The number of users could range from 50 to 200 within a single base station coverage area of 2000 m \(\times\) 2000 m. The number of base stations is a very large number, 10-30, which would be needed within this area to provide coverage due to the small cell sizes needed. For THz bands (\(>\)100 GHz), cell sizes are expected to be tens of meters or less. The number of users is typically 1-10 users within a single base  
station coverage area.