itter end, or both ends of the wireless link. Simple receive diversity, as shown in Figure 5.4, involves the use of two antennas that are placed sufficiently apart such that they can receive signals from independent signals paths. A basic way to select the optimal receive antenna output is switched diversity, where the receiver simply switches antennas whenever it detects weak signals or a high noise level from the current receiving level. More sophisticated diversity techniques such as maximum radio combining (MRC) receive on the multiple antennas simultaneously and apply the advanced signal processing algorithm to combine the different versions of the received signals to maximise the SNR. Switched diversity and MRC can be implemented on just the receive side of the link. The need for prior knowledge of the receiver in order to optimise the transmit paths makes transmit diversity more complicated. The simplest technique is to use the antenna from which information signals have arrived successfully from the target receiver. Hence multiple copies of the same information scheme are sent to the antenna for added redundancy. It can be seen that the same information signals must first be transformed into different RF signals to avoid interference with each other. All-IP Network Original message 101011 Received message 101011 Figure 5.5 Spatial multiplexing Diversity maximises the wireless range and coverage. It also increases the network throughput by finding quality signal paths to enable the devices to communicate using the highest data rates and avoiding the signal paths that are likely to produce packet errors and retransmissions. Spatial Multiplexing Mode Spatial multiplexing (SM) prospers in multipath environments as it allows the sender to transmit different portions of the user data on multiple paths in parallel in order to increase the system capacity, as shown in Figure 5.5. The target receiver must also implement a corresponding de-multiplexing algorithm to recover the original information stream from its r