Base station cooperation (BSC), also known as Cooperative Multi-Point (CoMP), has been identified as a key radio access technology for next-generation cellular networks. This work creates a foundational framework that extends BSC transmission to provide spatial spectrum sharing (SSS) through MIMO null beamforming while enjoying cooperative stream transmission. SSS is investigated by introducing the protected Gaussian MIMO broadcast channel (PGMBC), a GMBC with receive power constraints. Applications of the PGMBC are identified and its capacity region is derived. In addition, precoding schemes are developed to mitigate intercell interference and intersystem interference. The simulations show that through BSC, significant throughput gains over non-cooperative null-beamforming schemes can be achieved. However, to maximize the benefits of BSC in practical networks, the location and configuration of BS sites must be planned accordingly. This work introduces a fundamental framework for planning BSC networks. The impacts of BSC on coverage, capacity, complexity are investigated. In addition, a cell planning procedure for distributed, dynamic fractional BSC networks is described.