Protocol for transceiver initialization

Details Protocol for transceiver initialization Protocol for transceiver initialization

1999-11-23

2001-06-19

Chin, Stephen (Department: 2734)

Pulse or digital communications

Transceivers

C375S222000, C375S225000, C370S468000

Reexamination Certificate

active

06249543

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to data transmission systems and, more particularly, to transceiver initialization in data transmission systems.
2. Description of the Related Art
Data transmission systems which use multicarrier modulation have been receiving a lot of attention due to the high data transmission rates they offer. There are many different multicarrier modulation techniques that can be used in such systems. One popular multicarrier modulation technique is known as Discrete Multi Tone (DMT) modulation. Other multicarrier modulation techniques include Discrete Wavelet Multi Tone (DWMT) modulation and Orthogonal Frequency Division Multicarrier (OFDM) modulation.
One standard for high-speed data transmissions over twisted-pair phone lines that has developed is known as Asymmetric Digital Subscriber Lines (ADSL). The standard for ADSL is commonly known as T1E1 ADSL Standard of American National Standard Institute (ANSI). Another standard for high-speed data transmissions over twisted-pair phone lines that is presently proposed is known as Very High Speed Digital Subscriber Lines (VDSL).
FIGS. 1A and 1B
are basic exemplary diagrams of a transmitter and a receiver of a multicarrier modulation transmission system suitable for use with ADSL and VDSL.
FIG. 1A
is a block diagram of a conventional transmitter
100
for a multicarrier modulation transmission system. The transmitter
100
receives data signals to be transmitted at a buffer
102
. The data signals are then supplied from the buffer
102
to a forward error correction (FEC) unit
104
. The FEC unit
104
compensates for errors that are due to crosstalk noise, impulse noise, channel distortion, etc. The signals output by the FEC unit
104
are supplied to a data symbol encoder
106
. The data symbol encoder
106
operates to encode the signals for a plurality of frequency tones associated with the multicarrier modulation. In assigning the data, or bits of the data, to each of the frequency tones, the data symbol encoder
106
utilizes data stored in a transmit bit allocation table
108
and a transmit energy allocation table
110
. The transmit bit allocation table
108
includes an integer value for each of the carriers (frequency tones) of the multicarrier modulation. The integer value indicates the number of bits of data that are to be allocated to the particular frequency tone. The value stored in the transmit energy allocation table
110
is used to effectively provide fractional number of bits of resolution via different allocation of energy levels to the frequency tones of the multicarrier modulation. In any case, after the data symbol encoder
106
has encoded the data onto each of the frequency tones, an Inverse Fast Fourier Transform (IFFT) unit
112
modulates the frequency domain data supplied by the data symbol encoder
106
and produces time domain signals to be transmitted. The time domain signals are then supplied to a digital-to-analog converter (DAC)
114
where the digital signals are converted to analog signals. Thereafter, the analog signals are transmitted over a channel to one or more remote receivers.
FIG. 1B
is a block diagram of a remote receiver
150
for a conventional multicarrier modulation transmission system. The remote receiver
150
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)
152
. The ADC
152
converts the received analog signals to digital signals. The digital signals are then supplied to a Fast Fourier Transform (FFT) unit
154
that demodulates the digital signals while converting the digital signals from a time domain to a frequency domain. The frequency domain digital signals are then supplied to a frequency domain equalizer (FEQ) unit
156
. The FEQ unit
156
performs an equalization on the digital signals so the attenuation and phase are equalized over the various frequency tones. Then, a data symbol decoder
158
receives the equalized digital signals. The data symbol decoder
158
operates to decode the equalized digital signals to recover the data, orbits of data, transmitted on each of the carriers (frequency tones). In decoding the equalized digital signals, the data symbol decoder
158
needs access to the bit allocation information and the energy allocation information that were used to transmit the data. Hence, the data symbol decoder
158
is coupled to a received bit allocation table
162
and a received energy allocation table
160
which respectively store the bit allocation information and the energy allocation information that were used to transmit the data. The data obtained from each of the frequency tones is then forwarded to the forward error correction (FEC) unit
164
. The FEC unit
164
performs error correction of the data to produce corrected data. The corrected data is then stored in a buffer
166
. Thereafter, the data may be retrieved from the buffer
166
and further processed by the receiver
150
. Alternatively, the received energy allocation table
160
could be supplied to and utilized by the FEQ unit
164
. The received energy allocation table
160
could also be incorporated into the FEQ unit
164
.
The bit allocation tables and the energy allocation tables utilized in the conventional transmitter
100
can be implemented as a single table or as individual tables. Likewise, the bit allocation tables and the energy allocation tables utilized in the remote receiver
150
can be implemented as a single table or as individual tables. Also, the transmitter
100
is normally controlled by a controller, and the remote receiver
150
is normally controlled by a controller. Typically, the controllers are programmable controllers.
The transmitter
100
and the remote receiver
150
illustrated in
FIGS. 1A and 1B
, respectively, optionally include other components. For example, the transmitter
100
could add a cyclic prefix to symbols after the IFFT unit
112
, and the remote receiver
150
can then remove the cyclic prefix before the FFT unit
154
. Also, the remote receiver
150
can provide a time domain equalizer (TEQ) unit between the ADC
152
and the FFT unit
154
.
A data transmission system normally includes a central office and a plurality of remote units. Each remote unit communicates with the central office over a data link (i.e., channel) that is established between the central office and the particular remote unit. To establish such a data link, initialization processing is performed to initialize communications between the central office and each of the remote units. For purposes of the discussion to follow, a central office includes a central modem and a remote unit includes a remote modem. These modems are transceivers that facilitate data transmission between the central office and the remote unit. In general, the initialization processing for a multicarrier modulation transmission system includes the general operations of activation and acknowledgment of initialization requests, transceiver training at both the central office and the remote unit, exchange of rate requests between the central office and the remote unit, channel analysis, and exchange of transmitter settings (i.e., bit allocation tables) between the central office and the remote unit.
With respect to a multicarrier modulation transmission system in which a plurality of carriers (e.g., frequency tones) are used to transmit data between the central office and the remote unit, namely an ADSL system, the initialization processing conventionally carried out is known in the art. The T1E1 ADSL Standard describes an initialization process that transceivers must adhere to comply with this standard. The T1E1 ADSL Standard is hereby incorporated by reference.
FIGS. 1C and 1D
are flow diagrams of conventional initialization processing
170
. The initialization processing
170
is used to initialize communication links between a central office (CO) and a remote unit (RU). The initialization processing

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