Implementation concepts for distributed cooperative transmission

Information theory predicts huge performance gains in terms of spectrum efficiency by using cooperative transmission from multiple base stations. Cooperation eliminates inter-cell interference and it enables a higher channel rank. The isolated cell capacity is an upper bound for unlimited backbone capacity, infinite signal processing power and infinite channel feedback.We discuss a combined physical, medium access control (MAC) and network layer approach targeting minimal implementation loss while relaxing assumptions. It is based on frequency-selective channel quality identifier (CQI) reports to the serving station selecting the right user(s) on a given resource with best signal to interference and noise ratio (SINR). Such scheduling is performed independently in each cell. In adjacent cells it forms a group of users whose mutual interference is smaller than on average. The task of cooperative transmission is to further reduce the mutual interference within this group. In a multi-user system, the group shares only part of the spectrum. Feedback can hence be limited to the granted resource blocks. Based on virtual pilot sequences we reduce the pilot overhead and use a suitable mirror feedback scheme in addition. Altogether the feedback overhead is reduced by 2 orders of magnitude.