Signaling method in an ofdm multiple access system

The present application is a continuation of U.S. patent application Ser. No. 11/186,490, entitled “SIGNALING METHOD IN AN OFDM MULTIPLE ACCESS SYSTEM”, filed on Jul. 20, 2005, now pending, which is a divisional of U.S. patent application Ser. No. 09/805,887, entitled “SIGNALING METHOD IN AN OFDM MULTIPLE ACCESS SYSTEM”, filed on Mar. 15, 2001, now U.S. Pat. No. 7,295,509, which claims priority to U.S. Provisional Application No. 60/230,937, entitled “SIGNALING METHOD IN AN OFDM MULTIPLE ACCESS WIRELESS SYSTEM”, filed on Sep. 13, 2000, all of which are assigned to the assignee hereof, and expressly incorporated herein by reference.

This invention relates to an orthogonal frequency division multiplexing (OFDM) communication system, and more particularly to an OFDM communication system for a multiple access communication network.

Orthogonal frequency division multiplexing (OFDM) is a relatively well known multiplexing technique for communication systems. OFDM communication systems can be used to provide multiple access communication, where different users are allocated different orthogonal tones within a frequency bandwidth to transmit data at the same time. In an OFDM communication system, the entire bandwidth allocated to the system is divided into orthogonal tones. In particular, for a given symbol duration T available for user data transmission, and a given bandwidth W, the number of available orthogonal tones F is given by WT. The spacing between the orthogonal tones Δ is chosen to be 1/T, thereby making the tones orthogonal. In addition to the symbol duration T which is available for user data transmission, an additional period of time T_c can be used for transmission of a cyclic prefix. The cyclic prefix is prepended to each symbol duration T and is used to compensate for the dispersion introduced by the channel response and by the pulse shaping filter used at the transmitter. Thus, although a total symbol duration of T+T_c is employed for transmitting an OFDM symbol, only the symbol duration T is available for user data transmission and is therefore called an OFDM symbol duration.

In prior OFDM techniques, an OFDM signal is first constructed in the frequency domain by mapping symbols of a constellation to prescribed frequency tones. The signal constructed in the frequency domain is then transformed to the time domain by an inverse discrete Fourier transform (IDFT) or inverse fast Fourier transform (IFFT) to obtain the digital signal samples to be transmitted. In general, symbols of the constellation have a relatively low peak-to-average ratio property. For example, symbols of a QPSK constellation all have the same amplitude. However, after being transformed by the IDFT or IFFT, the resultant time domain signal samples are the weighted sum of all the symbols, and therefore generally do not preserve the desirable low peak-to-average ratio property. In particular, the resulting time domain signal typically has a high peak-to-average ratio.

Existing techniques for implementing OFDM communication systems can be highly inefficient due to the relatively high peak-to-average ratio when compared with other signaling schemes, such as single carrier modulation schemes. As a result, existing OFDM techniques are not well suited for a wireless multiple access communication network with highly mobile users because the high peak-to-average ratio of the transmitted signal requires a large amount of power at the base station and at the wireless device. The large power requirements result in short battery life and more expensive power amplifiers for handheld wireless communication devices or terminals. Accordingly, it is desirable to provide an OFDM technique which reduces the peak-to-average ratio of the signal to be transmitted, while simultaneously taking advantage of the larger communication bandwidth offered by an OFDM communication system.

In one aspect of the communication system, power consumption associated with generating and transmitting OFDM signals is reduced as compared to the prior OFDM systems discussed above. The OFDM signaling method includes defining a constellation having a plurality of symbols, defining the symbol duration for the OFDM communication signal, and defining a plurality of time instants in the symbol duration. In a given symbol duration, a plurality of tones in the symbol duration are allocated to a particular transmitter and the signal to be transmitted is represented by a vector of data symbols from the symbol constellation. The symbols are first directly mapped to the prescribed time instants in the symbol duration. A continuous signal is then constructed by applying continuous interpolation functions to the mapped symbols such that the values of the continuous signal at the prescribed time instants are respectively equal to the mapped symbols and the frequency response of the continuous signal only contains sinusoids at the allocated tones. Finally the digital signal, which is to be transmitted, consists of samples of the continuous signal. Alternatively, the digital signal can be generated directly by applying discrete interpolation functions to the mapped symbols. As symbols from the constellation generally have good peak-to-average ratio property, proper choices of allocated frequency tones, prescribed time instants and interpolation functions can result in a minimized peak-to-average ratio of the continuous function and the digital signal samples.

In one aspect, a digital processing system is defined that is utilized in a transmitter that generates a transmission signal having a first circuit that receives a discrete signal of complex data symbols, calculates a frequency response of the discrete signal, and outputs a first vector of length M, a second circuit that receives the vector of length M and generates a second vector of length N, wherein the second vector of length N includes elements of the first vector at positions corresponding to tones allocated to the transmitter, and a third circuit that receives the second vector and generates a digital time domain vector therefrom for transmission by the transmitter.

In one aspect, an apparatus that generates a transmission signal is defined which comprises means for receiving a discrete signal of complex data symbols, calculates a frequency response of the discrete signal, and outputs a first vector of length M, means for receiving the vector of length M and generates a second vector of length N, wherein the second vector of length N includes elements of the first vector at positions corresponding to tones allocated to a transmitter, and means for generating a digital time domain vector of the second vector for transmission by the transmitter.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of an OFDM system.

FIG. 2A is a block diagram of an interpolation system used by the OFDM system of FIG. 1.

FIG. 2B is a block diagram of another interpolation system used by the OFDM system of FIG. 1.

FIG. 3A is a graph showing symbols mapped to prescribed time instants in the time domain according to the OFDM technique implemented by the system of FIG. 1.

Continue reading about Signaling method in an ofdm multiple access system...
Full patent description for Signaling method in an ofdm multiple access system

Brief Patent Description - Full Patent Description - Patent Application Claims

Click on the above for other options relating to this Signaling method in an ofdm multiple access system patent application.
###


How KEYWORD MONITOR works... a FREE service from FreshPatents
1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored.
3. Each week you receive an email with patent applications related to your keywords.  
Start now! - Receive info on patent apps like Signaling method in an ofdm multiple access system or other areas of interest.
###


Previous Patent Application:
Optical disc manufacturing method, disc master manufacturing method, and optical disc
Next Patent Application:
Updating routing and outage information in a communications network
Industry Class:
Multiplex communications

###

Design/code © 2009 FreshContext LLC/Freshpatents.com. Website Terms and Conditions - Also read: About this Page
Patent data source: patents published by the United States Patent and Trademark Office (USPTO)
Information published here is for research/educational purposes only (and in conjunction with our Keyword Monitor) and is not meant to be used in place of the full USPTO patent document/images or a comprehensive patent archive search. Complete official applications are on file at the USPTO and often contain additional data/images (Freshpatents is currently text-only). FreshPatents.com is not affiliated with or endorsed by the USPTO or firms/individuals or products/designs/ideas related to listed patents.

FreshPatents.com Support
Thank you for viewing the Signaling method in an ofdm multiple access system patent info.
IP-related news and info


Results in 2.50598 seconds


Other interesting Feshpatents.com categories:
Daimler Chrysler , DirecTV , Exxonmobil Chemical Company , Goodyear , Intel , Kyocera Wireless , paws