WJCE6355 Intel, WJCE6355 Datasheet - Page 14

• Manufacturer Part Number: WJCE6355
• Description: Demodulator 64-Pin LQFP
• Manufacturer: Intel

Specifications of WJCE6355

• Package: 64LQFP
• Operating Temperature: -40 to 85 °C

Data Sheet
2.13
This module generates soft decisions for demodulated bits using the channel-equalized in-phase and quadrature compo-
nents of the data carriers as well as per-carrier channel state information (CSI). The de-mapping algorithm depends on the
constellation (QPSK, 16 QAM or 64 QAM) and the hierarchy (α = 0, 1, 2 or 4). Soft decisions for both low- and high-priority
data streams are generated.
2.14
The OFDM transmitter interleaves the bits within each carrier and also the carriers within each symbol. The de-interleaver
modules consist largely of memory to invert these interleaving functions and present the soft decisions to the FEC in the
original order.
2.15
The Viterbi decoder accepts the soft decision data from the OFDM demodulator and outputs a decoded bit-stream. The
decoder does the de-puncturing of the input data for all code rates other than 1/2. It then evaluates the branch metrics
and passes these to a 64-state path-metric updating unit, which in turn outputs a 64-bit word to the survivor memory.
The Viterbi decoded bits are obtained by tracing back the survivor paths in this memory. A trace-back depth of 128 is
used to minimize any loss in performance, especially at high code rates.
The decoder re-encodes the decoded bits and compares these with received data (delayed) to compute bit errors at its
input, on the assumption that the Viterbi output BER is significantly lower than its input BER.
2.16
The Viterbi decoded bit stream is aligned into 204-byte frames. A robust synchronization algorithm is used to ensure
correct lock and to prevent loss of lock due to noise impulses.
2.17
Errors at the Viterbi output occur in bursts and the function of the de-interleaver is to spread these errors over a number
of 204-byte frames to give the Reed-Solomon decoder a better chance of correcting these. The de-interleaver is a
memory unit which implements the inverse of the convolutional interleaving function introduced by the transmitter.
2.18
Every 188-byte transport packet is encoded by the transmitter into a 204-byte frame, using a truncated version of a
systematic (255,239) Reed-Solomon code. The corresponding (204,188) Reed-Solomon decoder is capable of correcting
up to eight byte errors in a 204-byte frame. It may also detect frames with more than eight byte errors.
In addition to efficiently performing this decoding function, the Reed-Solomon decoder in CE6355 keeps a count of the
number of bit errors corrected over a programmable period and the number of uncorrectable blocks. This information can
be used to compute the post-Viterbi BER.
2.19
The de-scrambler de-randomizes the Reed-Solomon decoded data by generating the exclusive-OR of this with a
pseudo-random bit sequence (PRBS). This outputs 188-byte MPEG transport packets. The TEI bit of the packet header
may be set if required to indicate uncorrectable packets.
2.20
MPEG data can be output in parallel or serial mode. The output clock frequency is automatically chosen to present the
MPEG data as uniformly spaced as possible to the transport processor. This frequency depends on the guard ratio,
constellation, hierarchy and code rate. There is also an option for the data to be extracted from the CE6355 with a clock
provided by the user.
14
De-Mapper
Symbol and Bit De-Interleaving
Viterbi Decoder
MPEG Frame Aligner
De-interleaver
Reed-Solomon Decoder
De-scrambler
MPEG Transport Interface
Intel Corporation
CE6355