Wireless communication systems are amongst the communication systems that have made use of advancements in digital communication technologies. A cellular communication system, for instance, is exemplary of a wireless communication system. While the early generation of wireless communication systems generally utilized analog communication techniques and provided for only limited data communication capabilities, newer-generation, wireless communication systems are exclusively using digital technologies, and increasingly provide for data-intensive communication services. As with any wireless communication system, noise, interference, signal distortions due to the limited channel bandwidth and non-linearity, time-variant multi-path propagation condition, and other impairments experienced during propagation alter the signal such that the data recovered in the receiver may differ with the corresponding data that are transmitted. This may generate errors in the recovery of the informational content of the data. And, if the impairment is too significant, the communications fail.
Significant efforts, therefore, are made to combat the impairments experienced during transmission. One promising technology in wireless communications under multi-path propagation conditions comprises the use of multiple transmit antennas and multiple receive antennas, to provide spatial diversity of propagation. To effectively exploit the spatial diversity, the digital symbols, carrying the information of data after modulation, are often encoded with space-time coding techniques before they are converted to RF signal for transmission.
In particular, space-time block coding (STBC) is one example of space-time coding techniques, for the purpose of improving the error rate performance. In a typical digital wireless communication system adopting space-time block coding, the data, which are in the form of binary bits and may have been encoded with other coding operations including error-correction coding, are digitally modulated (or equivalently, mapped) into digital symbols. Corresponding to particular values of the binary data, these digital symbols are selected, in general, from a constellation of complex values. In various existing communication systems, MPSK (M-ary Phase Shift Keying) and MQAM (M-ary Quaduature Amplitude Modulation) are widely-used, digital modulation techniques. In MPSK, where M is a power of two, each symbol takes a complex value from the constellation consisting of M points evenly distributed on a circle of unit radius. In MQAM, where M is a power of four, each symbol takes a complex value from the constellation consisting of M points evenly distributed on the grid lines of a square area with equal distance. Block by block, these symbols are then applied to a space-time block encoder. Then, the encoded symbols, after passing through pulse-shaping filters to limit the signal bandwidth, are converted to analog signals by A/D converter and then up-converted to RF signals, and then, are properly distributed to the multiple antennas for transmission.
Among various space-time block coding schemes, Alamouti coding is the simplest one applicable to a wireless communication system equipped with two transmit antennas and one or more receive antennas. With each code block of Alamouti code, the information carried by two symbols is transmitted in two time slots, and thus the coding rate is one. Another important virtue of Alamouti coding is that the optimum decoding in the receiver can be easily implemented with a simple linear detector.
In an Alamouti encoder, for each block, the encoder accepts two input symbols, and generates two sets of output symbols for transmission in two time slots, respectively, two output symbols per set for each time slot. The two output symbols transmitted in the first time slot, one from each antenna, are the same as the two input symbols. The two output symbols transmitted in the second time slot, one from each antenna, are the symbols formed by complex-conjugating the two input symbols, and then reversing the sign of one of the conjugated symbols. Moreover, after been up-converted to the RF (Radio Frequency) band, these output symbols are applied to the two transmit antennas in a manner such that each of the two input symbols, transmitted in the first time slot, and their conjugations, transmitted in the second time slot, are always transmitted from two different antennas. This is to say, for each code block, the information content carried by each symbol is transmitted twice using two time slots, once in the form of the symbol itself from one antenna, once in the form of its conjugation from another antenna.
Prior to being applied to transmit antennas, the output symbols of the Alamouti encoder are converted to analog signals and up-converted to form RF signals, and then the RF signals are amplified by power amplifiers (PA). In reality, a power amplifier is only able to amplify a signal within a limited dynamic range without, or with limited, non-linear distortion. Otherwise, if the signal amplitude varies in a dynamic range wider than the limit that the PA can handle, serious non-linear distortion results in the amplified signal. In general, the wider the signal dynamic range that a PA can handle without distortion, the more expensive the PA is. If a manner could be provided that utilizes a signal of reduced dynamic range, a less expensive PA, operable over a reduced dynamic range could instead be utilized.
It is in light of this background information related to the communication of data that the significant improvements of the present disclosure have evolved.
USPTO Backgrounds
USPTO Backgrounds