 Multi-antenna transmission schemes Bandwidth = 1 MHz. It can be observed that depending on the inverse carrier-to-noise ratio of each sub-channel, the amount of power allocated to each sub-channel differs, provided that the sum of sub- channel powers does not exceed the total available power. The power allocated to each sub-channel corresponds to parameters 22. 10.4.2 Spatial Multiplexing and Diversity The main objective of space-time diversity coding schemes is to exploit the inherent spatial (multi- path) diversity in MIMO channels through properly-designed space-time codes. In this section, two transmit diversity schemes, namely the Alamouti scheme and Cyclic Delay Diversity (CDD), are described where both realize full spatial diversity of the channel without requiring channel knowledge at the transmitter. In the Alamouti scheme, we consider a MIMO channel with two transmit antennas and any number of receive antennas. The Alamouti scheme can be described as follows. Two different complex-valued data symbols S1 and S2 are transmitted simultaneously from antenna ports 1 and 2, respectively, during the first symbol period. In the second symbol period, symbols - S2 and st are and are sent from antennas 1 and 2, respectively. It must be noted that the rate equals one in the Alamouti scheme since two independent data symbols are transmitted over two symbol periods. Let's consider the following case with two transmit-antennas and one receive-antenna, thereby we have two channels H and H2. The received signal at the first and second symbol period can be expressed as follows: (10-33) y2=-H1s*+H2s+n2 Letr = THE the relationship between the output and the input of the channel can be written as follows = Hs + n where multiplying both sides of the latter equation by HH yields r = HH + n. Since H is orthogonal; i.e., HHH = al where a = |H1|2 + | H2|2; dividing both sides of the equation by yields: (10-34) It is assumed that the channels are independent and identically distributed with frequency flat-fading and remain const