A MICROCELL MACROCELL CELLULAR ARCHITECTURE FOR LOW-MOBILITY AND HIGH-MOBILITY WIRELESS USERS

We explore the use of a wireless network having a two-tier architecture to serve both conventional mobile subscribers and quasi-stationary (e.g., PCN) subscribers. The latter are served by microcells which are embedded within macrocells that serve the mobile users. This provides a balance between maximizing the number of users per unit area (which favors small cells) and minimizing the network control associated with handoff (which favors large cells). We evaluate four approaches to sharing the spectrum between the two tiers, using per-cell capacity as our measure. The first two feature spread-spectrum sharing, i.e., they use TDMA among microcell users and CDMA among macrocell users (System 1), or vice versa (System II). The other two approaches feature orthogonal sharing, i.e., they use TDMA in both tiers, with time slots (System III) or frequency channels (System IV) partitioned so there is no overlap between tiers. Our analysis shows that the capacity tradeoffs are poor for Systems I and II because of the large amounts of cross-tier interference; and that System IV gives the best capacity tradeoffs. In addition, it permits graceful integration of new systems with existing ones, and can be generalized from the specific version treated here.