In this section, we briefly discuss the benefits of using MIMO architecture together with OFDM modulation and LDPC coding.

Wireless channels, in addition to the problem of fading, also suffer from the problem of inter-symbol-interference (ISI). ISI is caused by the reception of a small number of reflections from remote objects (as opposed to the large number of reflections from nearby objects that causes fading). ISI causes the receiver to receive the original signal, overlapped by some delayed versions of the signal (illustrated in Figure 5). Traditionally, different types of equalizers were used to reject ISI. However, the complexity of good equalizers is usually high, making their employment fairly problematic. OFDM modulation [4] provides a fairly strong and simple ISI rejection mechanism. It essentially introduces a guard interval in between symbols, in which the interference can reside without critically distorting the original signal. The use of OFDM modulation within MIMO structured systems creates a strong system that has the ability to successfully reject fading as well as ISI.

Figure 5: Wireless channel: ISI and fading problems
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The increased capacity of MIMO channels can be translated into increased throughput provided that proper coding is used prior to transmission. The coding procedure essentially pads the transmitted data with some protection bits that help the receiver decide whether errors occurred during transmission. LDPC codes are highly efficient (with respect to encoding and decoding complexity) capacity-approaching codes. Using LDPC codes helps to fulfill the high-throughput potential of MIMO systems in a highly efficient manner.

The upcoming IEEE 802.11n Wireless Local Area Networks (WLAN) standard uses MIMO architecture, along with OFDM and LDPC coding. The standard has the ability to provide a stunning throughput of up to 600 Mbps as apposed to 54 Mbps provided by the older, non-MIMO IEEE 802.11a standard.