In general, wireless communication systems transmit signals between transmitting antennas and receiving antennas. Because the location of transmitting and receiving antennas may be far apart, a transmitted signal often encounters a variety of mediums en route to a receiving antenna. For example, a transmitted signal may encounter mountains, buildings, and other mediums en route to a receiving antenna. Additionally, many transmitting and receiving antennas are mobile, e.g., cell phone antennas. As a result, a transmitted signal is often divided into a plurality of sub-signals, with each sub-signal having a unique path and time delay, en route to a receiving antenna. The existence of multi-path propagation requires special consideration when designing a wireless communication system. For example, at the receiving antenna, the original transmitted signal may be reconstructed by adding the sub-signals together.
In an effort to increase the data rate capacity of wireless communication systems, higher order modulation schemes, e.g., 16 QAM (quadrature amplitude modulation) or 8-PSK (phase shift keying), and spectrally efficient data allocation schemes have been developed. For example, 1x evolution data and voice (1xEV-DV), phase shift keying (8-PSK), and high speed downlink packet access (HSDPA) are standards that permit higher data transmission rates through the use of higher order modulation schemes and/or spectrally efficient data allocation schemes.
Unfortunately, using higher order modulation schemes (e.g. 16 QAM, 8-PSK) and spectrally efficient data allocation schemes make wireless communication systems undesirably sensitive to multi-path data propagation. In particular, multi-path data propagation may cause a loss of signal orthogonality resulting in data on one channel being more susceptible to interference from other channels and, thereby significantly decreasing data throughput of the wireless communication system. Therefore, methods and systems that overcome performance degradation due to multi-path data propagation, while permitting high data transfer rates are desirable.
USPTO Backgrounds
USPTO Backgrounds