Multiplex communications – Generalized orthogonal or special mathematical techniques – Quadrature carriers
Reexamination Certificate
1997-04-01
2001-01-16
O'Neill, Michael (Department: 3713)
Multiplex communications
Generalized orthogonal or special mathematical techniques
Quadrature carriers
C375S261000
Reexamination Certificate
active
06175550
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of The Invention
This invention relates to communication systems and, more particularly, OFDM (Orthogonal Frequency Division Multiplexing) modulation schemes which are suitable to provide a wide range of information transfer rates in a wide range of physical environments.
2. Description of Related Art
OFDM is a block-oriented modulation scheme that maps N data symbols into N orthogonal carriers separated by a distance of 1/T, where T is the block period. As such, multi-carrier transmission systems use OFDM modulation to send data bits in parallel over multiple, adjacent carriers (also called tones or bins). An important advantage of multi-carrier transmission is that inter-symbol interference due to signal dispersion (or delay spread) in the transmission channel can be reduced or even eliminated by inserting a guard time interval between the transmission of subsequent symbols, thus avoiding an equalizer as required in single carrier systems. This gives OFDM an important advantage over single carrier modulation schemes. The guard time allows delayed copies of each symbol, arriving at the receiver after the intended signal, to die out before the succeeding symbol is received. OFDM's attractiveness stems from its ability to overcome the adverse effects of multi-channel transmission without the need for equalization. A need exists for a flexible OFDM system which provides the advantages of OFDM to a variety of communication environments.
SUMMARY OF THE INVENTION
The scaleable OFDM system according to the principles of the present invention provides increased flexibility and adaptability by providing scaling of the operating parameters and/or characteristics for the OFDM system. For example, control circuitry can scale the transmission rate by scaling of the OFDM symbol duration, the number of carriers and/or the number of bits per symbol per carrier. Scaleability permits the scaleable OFDM system to operate in various communications environments requiring various operating parameters and/or characteristics. By scaling the operating parameters and/or characteristics of the OFDM system when control circuitry determines that different operating parameters and/or characteristics are necessary or advantageous, the control circuitry can dynamically change the operating parameters and/or characteristics, thereby providing compatibility or the desired performance. For example, by dynamically scaling the bit rate, widely varying signal bandwidths, delay spread tolerances and signal-to-noise ratio (SNR) requirements can be achieved. As such, a scaleable OFDM system is particularly suitable for application in mobile, wireless communication devices, which support a variety of services, in a variety of environments, indoor as well as outdoor and in radio channels with differing bandwidths.
In accordance with aspects of certain embodiments of the scaleable OFDM modulation system, a coded OFDM modulation system can be designed with an upper limit on the number of carriers and a variable symbol duration. The control circuitry can dynamically scale the number of carriers below the upper limit on the number of carriers to decrease the signal bandwidth and the transmission rate while delay spread tolerance remains the same. The control circuitry can also dynamically increase the symbol duration to decrease the transmission rate and the signal bandwidth and provide an increase in delay spread tolerance. In accordance with other embodiments, the scaleable OFDM modulation system achieves variable transmission rates using adaptive coding where different coding schemes are used to improve the link reliability and/or to decrease the peak-to-average power ratio.
In accordance with yet other embodiments of the scaleable OFDM modulation system, scaleable transmission rates permit asymmetric data rates between mobile units and base stations. For example, the mobile units can have lower data rates than the base stations by allocating only a fraction of the total number of carriers to each mobile, while the base stations transmit at all carriers simultaneously. Additionally, during data downloading for example, a mobile unit could have a larger downlink data rate than uplink data rate. In accordance with other aspects of a scaleable OFDM system, mobile units and base stations using the same antennas for both transmit and receive can benefit from adaptive antennas with any additional processing done at the base station, thereby keeping the mobile as simple as possible. The scaleable OFDM modulation system can use an adaptive antenna at the base by sending feedback through the uplink, for example, when channel characteristics of uplink and downlink are not identical.
REFERENCES:
patent: 5063574 (1991-11-01), Moose
patent: 5291289 (1994-03-01), Hulyalkar et al.
patent: 5748147 (1998-05-01), Bickley et al.
patent: 5757766 (1998-05-01), Sugita
patent: 5771224 (1998-06-01), Seki et al.
patent: 5822323 (1998-10-01), Kancko et al.
patent: 5848107 (1998-12-01), Philips
patent: 5952922 (1999-09-01), Shober
patent: 6009073 (1999-12-01), Kaneko
Lucent Technologies - Inc.
Nguyen Kim T.
O'Neill Michael
LandOfFree
Orthogonal frequency division multiplexing system with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Orthogonal frequency division multiplexing system with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Orthogonal frequency division multiplexing system with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2551019