Electrical computers and digital processing systems: memory – Addressing combined with specific memory configuration or... – For multiple memory modules
Reexamination Certificate
2000-04-12
2002-06-04
Bragdon, Reginald G. (Department: 2186)
Electrical computers and digital processing systems: memory
Addressing combined with specific memory configuration or...
For multiple memory modules
C708S404000, C370S210000
Reexamination Certificate
active
06401162
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to data transmission systems, and more particularly, to efficient processing of data within data transmission systems.
2. Description of the Related Art
Bi-directional digital data transmission systems are presently being developed for high-speed data communications. One standard for high-speed data communications over twisted-pair phone lines that has developed is known as Asymmetric Digital Subscriber Lines (ADSL). Another standard for high-speed data communications over twisted-pair phone lines that is presently proposed is known as Very High Speed Digital Subscriber Lines (VDSL).
The Alliance For Telecommunications Information Solutions (ATIS), which is a group accredited by the ANSI (American National Standard Institute) Standard Group, has finalized a discrete multi-tone based approach for the transmission of digital data over twisted-pair phone lines. The standard, known as ADSL, is intended primarily for transmitting video data and fast Internet access over ordinary telephone lines, although it may be used in a variety of other applications as well. The North American Standard is referred to as the ANSI T1.413 ADSL Standard (hereinafter ADSL standard), and is hereby incorporated by reference. Transmission rates under the ADSL standard are intended to facilitate the transmission of information at rates of up to 8 million bits per second (Mbits/s) over twisted-pair phone lines. The standardized system defines the use of a discrete multi-tone (DMT) system that uses 256 “tones” or “sub-channels” that are each 4.3125 kHz wide in the forward (downstream) direction. In the context of a phone system, the downstream direction is defined as transmissions from the central office (typically owned by the telephone company) to a remote location that may be an end-user (i.e., a residence or business user). In other systems, the number of tones used may be widely varied.
The ADSL standard also defines the use of reverse transmissions at a data rate in the range of 16 to 800 Kbit/s. The reverse transmissions follow an upstream direction, as for example, from the remote location to the central office. Thus, the term ADSL comes from the fact that the data transmission rate is substantially higher in the downstream direction than in the upstream direction. This is particularly useful in systems that are intended to transmit video programming or video conferencing information to a remote location over telephone lines.
Because both downstream and upstream signals travel on the same pair of wires (that is, they are duplexed) they must be separated from each other in some way. The method of duplexing used in the ADSL standard is Frequency Division Duplexing (FDD) or echo canceling. In frequency division duplexed systems, the upstream and downstream signals occupy different frequency bands and are separated at the transmitters and receivers by filters. In echo cancel systems, the upstream and downstream signals occupy the same frequency bands and are separated by signal processing.
ANSI is producing another standard for subscriber line based transmission system, which is referred to as the VDSL standard. The VDSL standard is intended to facilitate transmission rates of at least about 6 Mbit/s and up to about 52 Mbit/s or greater in the downstream direction. Simultaneously, the Digital, Audio and Video Council (DAVIC) is working on a similar system, which is referred to as Fiber To The Curb (FTTC). The transmission medium from the “curb” to the customer is standard unshielded twisted-pair (UTP) telephone lines.
A number of modulation schemes have been proposed for use in the VDSL and FTTC standards (hereinafter VDSL/FTTC). For example, some of the possible VDSL/FTTC modulation schemes include multi-carrier transmission schemes such as Discrete Multi-Tone modulation (DMT) or Discrete Wavelet Multi-Tone modulation (DWMT), as well as single carrier transmission schemes such as Quadrature Amplitude Modulation (QAM), Carrierless Amplitude and Phase modulation (CAP), Quadrature Phase Shift Keying (QPSK), or vestigial sideband modulation.
Most of the proposed VDSL/FTTC transmission schemes utilize frequency division duplexing of the upstream and downstream signals. One particular proposed VDSL/FTTC transmission scheme uses periodic synchronized upstream and downstream communication periods that do not overlap with one another. That is, the upstream and downstream communication periods for all of the wires that share a binder are synchronized. With this arrangement, all the very high speed transmissions within the same binder are synchronized and time division duplexed such that downstream communications are not transmitted at times that overlap with the transmission of upstream communications. This is also referred to as a (i.e. “ping pong”) based data transmission scheme. Quiet periods, during which no data is transmitted in either direction, separate the upstream and downstream communication periods. When the synchronized time division duplexed (TDD) approach is used with DMT it is often referred to as synchronized DMT (SDMT).
A conventional transmitter for a multicarrier modulation system encodes data onto each of a plurality of frequency tones, and then modulates the frequency domain data supplied by the data symbol encoder with an Inverse Fast Fourier Transform (IFFT) unit to produce time domain signals to be transmitted. The time domain signals are then supplied to a digital-to-analog converter (DAC) where the analog signals are converted to digital signals. Thereafter, the digital signals are transmitted over a channel to one or more remote receivers.
A conventional remote receiver for a multicarrier modulation system. The remote receiver receives analog signals that have been transmitted over a channel by a transmitter. The received analog signals are supplied to an analog-to-digital converter (ADC) which produces digital signals. The digital signals are then supplied to a Fast Fourier Transform (FFT) unit that demodulates the digital signals while converting the digital signals from a time domain to a frequency domain. The demodulated digital signals are then supplied to a data symbol decoder to recover the data, or bits of data, transmitted on each of the carriers (frequency tones).
Transceivers (transmitters and receivers) implementing multicarrier modulation typically have significant processing and memory requirements. Typically, the processing requirements are carried out by digital signal processing. In one implementation the multicarrier modulation is performed by processing by a Fast Fourier Transform (FFT) processor or an Inverse Fast Fourier Transform (IFFT) processor. Often, the FFT/IFFT processor is implemented by a digital signal processor (DSP). It is known that FFT/IFFT computations require that the processing interact with a plurality of data points simultaneously. FFT/IFFT computations are thus complicated processing operations that simultaneously use a plurality of data points that are not sequential.
As a result, in conventional designs, the FFT/IFFT processor is required to have numerous ports which connect to numerous ports of a memory system. Further, the outputs of the FFT/IFFT processor was in most cases hardwired back the memory system where the output values were stored. In general, the conventional designs require that the FFT/IFFT processor be able to access any location in the memory system at any time, which required numerous ports and complex wiring. Thus, conventional designs are costly due to the numerous ports required as well as due to the complex hardwiring required.
One improvement to the conventional designs that has been done is to use “in-place” processing so as to make efficient use of the memory system. In-place processing efficiently uses available memory by storing computed values in the locations from which the data values (used to produce the computed values) were originally retrieved. In other words, by using an in-place processing technique, the overall size of
Amati Communications Corporation
Beyer Weaver & Thomas LLP
Bragdon Reginald G.
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