onally among mobile stations in the collaborative zone. The inter-BS information exchange and joint processing, by enabling macro-diversity combining, soft decision information in the form of log-likelihood ratios are generated at the neighbor base stations, transmitted to anchor BS accompanied with scheduling information through M-SAP or C-SAP primitives over the core network, and combined at the anchor BS. Using cooperative beamforming, the quantized versions of received signals are generated at neighbor base stations, transmitted to the anchor BS accompanied with channel state information and scheduling information through M-SAP or C-SAP primitives over backhaul and jointly processed at the anchor BS. 10.8 INTERFERENCE MITIGATION Fractional Frequency Reuse (FFR) is an interference mitigation scheme which allows the use of different frequency reuse factors over different frequency partitions in certain time intervals in downlink and uplink transmissions. The FFR is usually combined with other schemes such as power control or multi-BS MIMO technologies for adaptive control and joint optimization. The power control and multi-BS MIMO interference mitigation schemes were described in previous sections. In a generic FFR scheme as shown in Figure 10-48, the sub-carriers over the entire transmission band- width are grouped into frequency partitions with different reuse factors. In general, the received signal quality can be improved by assigning the mobile stations in the frequency partitions with a higher frequency reuse factor due to lower interference levels. This will benefit the mobile stations near the cell edge or the mobile stations that are suffering from severe inter-cell interference. The BS may apply a lower frequency reuse factor to some frequency partitions in order to serve the mobile stations which do not experience significant inter-cell interference, resulting in an improvement in spectral efficiency. The resource allocation when using the FFR scheme may take several factors into consideration, inclu