or subscriber devices. Beamforming known as Advanced Antenna System uses multiple antennas to transmit weighted signals to improve the coverage and capacity of the system and reduce outage probability. When receiving a signal, beamforming can increase the receiver sensitivity in the direction of the wanted signals and decrease the sensitivity in the direction of interference and noise. Beamforming techniques such as EBF and MRT are defined as optional features in the IEEE 802. 16e WiMAX standard [8]. Receive diversity and transmit diversity do not require direct support from WiMAX standards but transmit diversity has been put forward as a requirement by WiMAX Forum. Downlink 2x2 open loop MIMO and uplink collaborative MIMO are defined in WiMAX Forum Wave 2 certification as mandatory features of the terminals. Closed loop MIMO is not part of Wave 2 [9]. The certification process is explained in section 4.6. 4.3.2 Fractional Frequency Reuse Mobile WiMAX supports frequency reuse of one (N = 1) as compared to no reuse in 802.16d. The N = 1 means that all cell/sectors operate on the same frequency channel to maximize spectral efficiency. However, due to heavy co-channel interference (CCI) with N = 1, users at the cell edge can suffer signal degradation. To address this issue, the reuse pattern of sub-channels within a channel can be configured SO that users close to the base station operate with all the sub-channels available while the users at the edge use only a fraction of all sub-channels available, which is known as Fractional Frequency Reuse In Figure 4.9, fractional frequency reuse can be applied by utilizing frequency reuse 1x3x1 near the center and frequency reuse 1x3x3 near the cell edges. F1, F2 and F3 represent different sets of sub-channels in the same frequency channel. There is no need for detail frequency planning and is very flexible to 1x3x1 Frequency Reuse F=F1+F2+F3 F1=F, Subchannel {0, N-1} F2 = F, Subchannel {N, 2N-1} F3 = F, Subchannel {2N, 3N-1} 1x3x3 Frequency Reuse Figure 4.9 Fractional frequ