Overview Architectures of Smart Antenna (MIMO) One of the biggest problems in wireless telecommunication is fading and inter-symbol interferences as shown in the diagram, below. Fading refers to the distortion of intensity over certain propagation media and Inter-symbol interference (ISI) occurs when there is reflection caused by other remote objects. The transmitted signal, at the receiver end are overlapped and delayed. To overcome this problem we use MIMO architecture, Orthogonal Frequency-Division Multiplexing (OFDM) modulation and Low-Density Parity-Check (LDPC) coding. MIMO operate in two modes diversity mode and spatial multiplexing mode to solve the problem. Diversity Mode The use of two or more antennas that are spaced sufficiently apart such that they can receive signals from independent signal paths are involve in a Simple Receive Diversity. A basic way to select an optimal receive antenna from an array of antennas is Selection Combining, whereby the receiver switches to another antenna whenever it detects weak signals or a high noise level from the current receiving antenna. More sophisticated techniques such as Maximum Ratio Combining (MRC) receive on multiple antennas simultaneously and apply advanced signal processing algorithms to combine the different versions of the received signals to maximize SNR and minimize receive errors. Selection Combining and MRC can be implemented on just the receive side of the link as shown in the figure below. (Video54, 2008, p3) Spatial Multiplexing Mode In rich multipath environments with multiple uncorrelated signal paths as figure 5, Spatial Multiplexing (SM) allows the sender to transmit different portions of the user data on multiple paths in parallel to increase capacity. The target receiver must implement a corresponding de-multiplexing algorithm to recover the original information stream from multiple antennas. In an ideal multipath environment, SM can increase the capacity of a single frequency channel linearly with the number of transmit antennas used. (Video54, 2008, p4) Figure 5: Spatial diversity (Video54, 2008, p4) Spatial Multiplexing requires the same multiplexing algorithm on both sides of a communications link. Therefore it is not interoperable with existing 802.11a/b/g devices. Until 802.11n is defined, only SM client and SM network devices from the same vendor can communicate with each other. (Video54, 2008, p4)>