Base Station Location and Service Assignment in W-CDMA Networks

1. Base Station Location and Service Assignment in W-CDMA Networks Joakim Kalvenes1 Jeffery Kennington2 Eli Olinick2 Southern Methodist University 1Edwin L. Cox School of Business 2School of Engineering

2. Wireless Network Design: Inputs • Potential locations for radio towers (cells) • “Hot spots”: concentration points of users/subscribers (demand) • Potential locations for mobile telephone switching offices (MTSO) • Locations of access point(s) to Public Switched Telephone Network (PSTN) • Costs for linking towers to MTSOs, and MTSOs to PSTN

3. Wireless Network Design: Problem • Determine which radio towers to build (base station location) • Determine how to assign subscribers to towers (service assignment) • Determine which MTSOs to use • Maximize profit: revenue per subscriber served minus infrastructure costs

4. Wireless Network Design Tool

5. Code Division Multiple Access (CDMA)Technology • The basis for 3G cellular systems • Channel (frequency) allocation is not an explicit issue since the full spectrum is available in each cell • New calls cause incremental noise (interference) • New calls admitted as long as the signal-to-noise ratio stays with in system limit • Power transmitted by handset depends on distance to assigned radio tower • Tower location and assignment of customer locations to towers must be determined simultaneously

6. Tower 3 Power Control Example Received signal strength must be at least the target value Ptar Signal is attenuated by a factor of g13 Subscriber at Location 1 Assigned to Tower 3

7. Signal-to-Interference Ratio (SIR) Tower 3 Tower 4 Subscriber at Location 1 assigned to Tower 3 Two subscribers at Location 2 assigned to Tower 4

8. Constants and Sets Used in the Model • L isthe set of candidate tower locations. • M isthe set of subscriber locations. • gmℓis the attenuation factor from location m to tower ℓ. • is the set of tower locations that can service customers in location . • is the set of customer locations that can be serviced by tower ℓ.

9. More Constants and Sets Used in the Model • dmis the demand (channel equivalents) in location • r is the annual revenue generated per channel. • is the FCC mandated minimum service requirement. • is the cost of building and operating a tower at location . • SIRminis the minimum allowable signal-to-interference ratio. • s = 1 + 1/SIRmin.

10. Decision Variables Used in the Model • yℓ =1 if a tower is constructed at location ℓ; and zero, otherwise. • The integer variable xmℓ denotes the number of customers (channel equivalents) at that are served by the tower at location • The indicator variable qm =1 if and only if location m can be served by at least one of the selected towers.

11. Integer Programming Model The objective of the model is to maximize profit: subject to the following constraints:

12. Integer Programming Model

13. Quality of Service (QoS) Constraints • For known attenuation factors, gml, the total received power at tower location ℓ, PℓTOT , is given by • For a session assigned to tower ℓ • the signal strength is Ptarget • the interference is given by PℓTOT – Ptarget • QoS constraint on minimum signal-to-interference ratio for each session (channel) assigned to tower ℓ:

14. Quality of Service (QoS) Constraints