and E1 (2.048 Mbps) leased lines are the most common form of backhaul in rest of the world. Several technologies that can be used for the backhaul network are discussed in this section. 7.3.1 Performance Enhancements in Microwave Radios The microwave links are both point to point and point to multipoint and typically operate in frequencies below 40 GHz. The three enhancements that we are coming to see more frequently are in the areas of topology, modulation and support for IP. Point to multipoint in terms of topology; adaptive modulation in response to higher capacities, and Ethernet interfaces to support IP traffic. Some details on these enhancements are as follows. 7.3.1.1 Point to Multipoint (PMP) PMP Wireless backhaul solutions have been around for the last few years but are not as such in much use. These solutions can carry ATM, E1/T1, and IP traffics. In addition to unlicensed 2.4 and 5.8 GHz frequencies, PMP solutions are also available in 10.5, 26, and 38 frequency bands. The standard microwave propagation and prediction methods can also be used for PMP radios. Next Generation Mobile Communications Ecosystem 256 QAM 256 QAM 128 QAM 64 QAM 32 QAM Real-time 16 QAM QPSK Traffic Non real-time Traffic Figure 7.2 Adaptive modulation with changing weather conditions 7.3.1.2 Adaptive Modulation Adaptive Modulation or Dynamic Modulation refers to automatic adjustment of modulation pertaining to radio conditions. A microwave system that supports this feature can dynamically alter the modulation technique to maximize capacity at any given time. It switches up or down the modulation scale perhaps from 256 QAM (Quadrature Amplitude Modulation) to QPSK (Quadrature Phase Shift Keying) according to changing weather conditions (Figure 7.2). Unlike existing solutions that need several seconds to adjust themselves due to changing weather conditions; the switchover with adaptive modulation is implemented using a Hitless algorithm with zero down time. Microwave vendors are also claiming that dynamic modulation does not affect