FIGURE 5.67 Optimal combining performance for various number of CCIs.
5.3 TRANSMIT SPATIAL ANTENNA DIVERSITY TECHNIQUES
In this section, we will discuss a technique called transmit diversity. In the previous sections, we have
shown how using receive diversity can dramatically improve system performance. This improvement
comes at the expense of receiver complexity (i.e., power consumption, size, cost, and so on). Transmit
diversity aims to provide the similar benefits of having receive diversity, but will accomplish this by
transmitting with multiple antennas [73??“77].
In 1998, a simple space-time block code was presented by Alamouti, showing that 2 transmit
antennas and 1 receive antenna provide the same improvement order of MRC with 1 transmit and 2
receive antennas [78]. This technique was later adopted into the WCDMA UMTS and IS-2000 digital
cellular standards and is named Space-Time Transmit Diversity (STTD).
5.3.1 Space-Time Block Code (STBC)
As the name STBC implies, this technique involves grouping bits to be transmitted into a block of
data. This block will then be transmitted by being spread out over time and space, hence the name
Space-Time.
Space-Time Transmit Diversity. In this section, we will present the technique originally proposed
by Alamouti and later adopted by WCDMA UMTS.
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