eceiver antenna. SM requires uncorrelated multipaths. Since multipath fades change moment by moment with motion, there is no assurance that the uncorrelated signal path can always be found. Furthermore, SM does not works well in low SNR environments where signals are weakened by distance or the noise level from the RF and channel interference is high, thereby making it more difficult for the sender and receiver to identify the uncorrelated signal paths. When the SM is not possible then the MIMO system returns to the diversity mode. Another powerful concept for this is that of spatial diversity. In the presence of random fading caused by multipath propagation, the probability of losing the signal decreases exponentially with the number of de-correlated antenna elements being used. A key concept here is that of diversity order, which is defined by the number of correlated spatial branches available at the transmitter or the receiver. When combined together the linear array improves the coverage range versus quality trade-off offered to the wireless user. In an MIMO link, the benefits of the conventional antennas are retained since the optimisation of multiantenna systems are carried out in a larger space, thus providing additional degrees of freedom. These MIMO systems can provide a joint transmit-receive diversity gain as well as an array gain when the antenna elements are coherently combined. 5.6 All-IP Network For communication and networking purposes a large number of protocols are being used, but the IP (Internet protocol) provides a universal network layer protocol for wired packet networks and brings into play the same role in wireless systems. An all-IP wired and wireless network can make wireless networks more robust, scalable and cost-effective. It allows software and applications developed for wired IP networks to be employed on the wireless IP networks at present, most of the different wireless systems, such as PANs (permanent access networks), WANs and wide area cellular networks, are not compatible wi