ST70135 datasheet(12/29 Pages) STMICROELECTRONICS

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ST70135A

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In the transmit direction, the mapper receives a bit

stream from the Trellis encoder and modulates

the bit stream on a set of carriers (up to 256). It

generates coordinates for 2n QAM constellation,

where n < 15 for all carriers.

The Mapper performs the inverse operation,

mapping a block of bits into one constellation

point (in a complex x+jy representation) which is

passed to the IFFT block. The Trellis Encoder

generates

redundant

bits

improve

the

robustness

the

transmission,

using

4-Dimensional Trellis Coded Modulation scheme.

This

feature

can

disabled.The

Monitor

computes error parameters for carriers specified

in the Demapper process.

Those parameters can be used for updates of

adaptive

filters

coefficients,

clock

phase

adjustments, error detection, etc. A series of

values is constantly monitored, such as signal

power, pilot phase deviations, symbol erasures

generation, loss of frame, etc.

Generic TC Layer Functions

These functions relate to byte oriented data

streams. They are completely described in ANSI

T 1.4 13. Additions described in the Issue 2 of this

specification are also supported.

The data received from the demapper may be

split into two

paths, one dedicated to an

interleaved data flow the other one for a fast data

flow. No external RAM is needed for the

interleaved path.

The

interleaving/deinterleaving

used

increase the error correcting capability of block

codes for error bursts. After deinterleaving (if

applicable), the data flow enters a Reed-Solomon

error correcting code decoder, able to correct a

number of bytes containing bit errors. The

decoder also uses the information of previous

receiving stages that may have detected the error

bytes and have labelled them with an ”erasure

indication”. Each time the RS decoder detects and

corrects errors in a RS codeword, an RS

correction event is generated.

The occurrence of such events can be signalled to

the management layer.After the RS decoder, the

corrected byte stream is descrambled in the PMD

(Physical Medium Dependent) descramblers. Two

descramblers are used, for interleaved and

non-interleaved data flows.

These

are

defined

ANSI

T1.413.

After

descrambling, the data flows enter the Deframer

that extracts and processes bytes to support

Physical layer related functions according to ANSI

T1.413.

The

ADSL

frames

indeed

contain

physical layer-related information in addition to

the data passed to the higher layers. In particular,

the deframer extracts the EOC (Embedded

Operations Channel), the AOC (ADSL Overhead

Control) and the indicators bits and passes them

to the appropriate processing unit (e.g. the

transceiver controller).

The deframer also performs a CRC check (Cyclic

Redundancy Check) on the received frame and

generates events in case of error detection.Event

counters can be read by management processes.

The outputs of the deframer are an interleaved

and a fast data streams. These data streams can

either carry ATM cells or another type of traffic. In

the latter case, the ATM specific TC layer

functional block, described hereafter, is bypassed

and the data stream is directly presented at the

input of the interface module.

Figure 6 : Generic TC Layer Functions

DATA PATX MERGER

INTERLEAVER

DE-INTERLEAVER

CODING

PMD

SCRAMBLER

PMD

SCRAMBLER

DECODING

FRAMER

DEFRAMER

ATM

IndicationBits

AOC EOC

To/From

Demapper

FAST

DESCRAMBLER

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