Power control and cell site location technique for cdma systems with hierarchical architecture

Abstract

Multiple microcell base stations are located within a macrocell having single macrocell base station in an hierarchical architecture, and microcell users (&mgr;-users) and macrocell users (M-users) communicate respectively with the &mgr;-base and the M-base using the same frequency band, by appropriately (a) selecting the ratio of the radius r of each &mgr; cell and the average distance d from the M-base (r and d are measured by the “radio distance”, which includes the effects of shadowing), and (b) controlling the power level with which uplink (mobile to base) and downlink (base to mobile) messages are communicated. Typically, &mgr;-cell size and location are chosen such that d/r>10. With respect to uplink communications, the transmit powers of the &mgr;-users in a &mgr;-cell are controlled so that the total received power at the nearest M-base is equivalent to the received power from C M-users, where C is usually set to unity. As a result, the M-cell basically loses C users worth of capacity, but the total number of users is increased by virtue of the additional &mgr;-users. With respect to downlink communications, as long as the microbase and the macrobase are coordinated systems, the &mgr;-base transmit power is controlled so that at the point of handoff between a &mgr;-base and M-base, the received power at a user from the two bases is equivalent, and the received power at the bases from this user is also equivalent. With this arrangement, the &mgr;-base transmit power is increased as r grows and d decreases in order for this balance to occur. Where the M-base and &mgr;-base have no knowledge of each other and handoffs are not allowed between the two base types, a family of I/Q short codes which are quasi-orthogonal to the existing short (pilot) codes are generated, and these codes are used to distinguish between the M-base and &mgr;-base signals.