Multiplex communications – Generalized orthogonal or special mathematical techniques – Quadrature carriers
Reexamination Certificate
2001-01-16
2004-04-13
Rao, Seema S. (Department: 2666)
Multiplex communications
Generalized orthogonal or special mathematical techniques
Quadrature carriers
C370S476000, C370S510000, C375S260000, C375S298000, C375S364000
Reexamination Certificate
active
06721267
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to multi-carrier communication systems, including but not limited to radio frequency (RF) communication systems. More particularly, this relates to a scalable pattern methodology for multi-carrier communication systems.
BACKGROUND OF THE INVENTION
Multi-carrier communication systems are well known in the art. Pursuant to many such systems, an information-bearing signal, such as serial digitized voice or digital data is subdivided into a plurality of bit streams, each of which is encoded into symbols (e.g., BPSK, QPSK, 16QAM symbols) to form a corresponding plurality of symbol streams. Synchronization and pilot symbols are inserted into each of the plurality of symbol streams, yielding a plurality of composite symbol streams. The composite symbol streams are used to modulate separate carrier signals, yielding a corresponding plurality of sub-channels each occupying a discrete frequency band and carrying a portion of the information in the original information-bearing signal. The plurality of sub-channels are combined into a composite signal that is transmitted over an RF channel from a first location to a second location. At the second location, a receiver performs generally the inverse operations, demodulating and detecting each sub-channel separately. Pilot interpolation is performed to determine the carrier's phase and to estimate the effects of channel impairments, such as fading, multi-path effects, etc., and errors are corrected to overcome the effect of the channel impairments and reconstruct the original information signal.
As is known in the art, multi-carrier communication systems can be time division multiple access (TDMA) communication systems. In a TDMA system, a RF channel is shared among multiple users by dividing it into blocks of time. The blocks of time, commonly referred to as time slots, can then be assigned to different users. In most TDMA systems, the length of each slot and the channel bandwidth are fixed so that the same amount of information is sent in each slot. Because of this, the transmitter and receiver are usually configured to work with fixed amounts of information. For example, if the information being transmitted represents a voice conversation, the voice encoder that converts the voice signal into digital information will output the digital information in fixed length blocks and the decoder at the receiver will convert fixed length blocks of data back into voice. As another example, error control coding can be done to correct for symbol errors caused by the RF channel. At the transmitter, the digital information to be transmitted is encoded. At the receiver the received digital information is decoded in such a way as to correct for errors. The encoder/decoder operations are often designed to operate on fixed length blocks of data.
Generally, the amount of information that may be carried by any communication system in a fixed length time slot is a function of the available bandwidth. One of the advantageous aspects of multi-carrier communication systems is that different channel types (e.g., having different bandwidths) may be accommodated by increasing or decreasing the number of sub-channels, to the extent that the bandwidth of the total number of sub-channels does not exceed the available bandwidth. However, if the bandwidth of the signal is scaled without changing the length of the TDMA time slots, the amount of digital information carried by the time slots would be changed. This would require the redesign of parts of the communication system such as the voice and error control coding.
Accordingly, there is a need for a method of defining TDMA time slot structures usable in a multi-carrier communication system that scale readily between different numbers of sub-channels and different corresponding bandwidths without significantly changing the amount of digital information sent in each TDMA time slot so as not to require redesign of parts of the communication system such as the voice and error control coding. The present invention is directed to satisfying or at least partially satisfying these needs.
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Wong, et al. Multiuser OFDM with Adaptive Subcarrier, Bit and Power Allocation, IEEE, vol. 17, No. 18, Oct. 1999, pp. 1747-1758.
Doberstein Kevin G.
Hiben Bradley M.
Logalbo Robert D.
Newberg Donald G.
Duong Frank
Hughes Terri S.
Motorola Inc.
Rao Seema S.
Santema Steve R.
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