Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1998-03-30
2001-10-30
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S465000, C375S135000
Reexamination Certificate
active
06310870
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of high speed data communications, and more specifically, to the field of transmitting high speed data utilizing a low speed data wireless telecommunications medium.
One of the primary standard specifications relevant to the present invention is TIA/EIA/IS-95-A “Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System.” This code division multiple access (CDMA) industry standard is considered understood by those reasonably skilled in the art of the present invention.
According to the TIA/EIA/IS-95-A standard, a single data channel in the CDMA system can transmit a maximum of 9600 bits (binary digits) of information per second. While this data rate is sufficient for communicating voice information, the data throughput required for digital data transmission is considerably higher. In transmitting digital data, it is often the case that the higher the data rate the better.
One proposed solution combines multiple low data rate channels into a single high data rate channel, thereby exploiting the ability of CDMA systems to combine data signals into a common signal and then later extracting the original data from the common signal. This proposed solution simply modulates the data from each individual data channel by a slightly different phase angle and combines the data from each individual data channel into a high data rate channel. However, by requiring that each data channel be modulated by a modulating signal with a slightly different phase angle, this proposed solution places severe performance requirements upon the analog portion of the CDMA system. For example, if the CDMA system is attempting to combine eight data channels, the difference in the phase angles of the modulating signals cannot be more than 180/8 or 22.5 degrees. In general, the difference in the phase angles of the modulation signals is equal to 180
degrees where n is the number of individual data channels being combined. In actual practice, due to the difficulties of designing the analog hardware that can perform adequately with such a small phase angle difference, the number of different phase angles used is small. In order to provide a high data rate channel, i.e., combine a large number of low data rate channels, the proposed solution shares the same phase angle between different data channels, leading to a loss of processing gain, hence an overall reduction in the signal to noise ratio.
There is, therefore, a need in the industry for a system addressing these and other related and unrelated problems.
SUMMARY OF THE INVENTION
The present invention provides for a system to achieve a high data rate channel in a CDMA system. According to the preferred embodiment, multiple CDMA data sequences are modulated in parallel by multiple low data rate CDMA channels. Each low data rate CDMA channel digitally delays the CDMA data sequence modulated thereby by a different period of time, where the largest period of time of all the digital delays is less than one-half the period of a single chip of data. The high data rate CDMA channel is created by combining the output of multiple low data rate CDMA channels operating in parallel, thereby resulting in significantly increased data throughput.
After combining the multiple, time delayed, low data rate CDMA channels, the high data rate channel is converted into an analog signal and transmitted over the air. At the receiver side, the received analog signal is converted back into a digital signal and decoded to extract the individual low data rate CDMA channels.
According to the first preferred embodiment of the present invention, each of the individual low data rate CDMA channels are delayed by varying amount of time before being combined into a single high data rate CDMA channel. One of the low data rate CDMA channels, typically the first CDMA channel, is delayed with a delay unit of value zero or effectively no delay.
According to the first preferred embodiment of the present invention, the quadrature (Q) channel data sequence is delayed one half chip period with respect to the in-phase (I) channel data sequence.
According to the first preferred embodiment of the present invention, all I channel data sequences are modulated by a same frequency carrier while all Q channel data sequences are modulated by a same frequency carrier, but different from the carrier modulating the I channel data sequence.
Thus, the present invention provides a system for combining multiple low data rate CDMA channels into a single high data rate CDMA signal without requiring the addition and use of complex analog hardware. An arbitrary number of CDMA channels are combined into a single high data rate CDMA channel through the use of general purpose digital hardware and simple delay elements. Objects, features, and advantages of the present invention will become apparent upon reading and understanding the present specifications, when taken in conjunction with accompanying drawings.
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Nguyen Chau
Oki Telecom, Inc.
Thomas Kayden Horstemeyer & Risley LLP
Trinh D.
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