Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
1999-09-30
2004-09-21
Tran, Khai (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C714S755000
Reexamination Certificate
active
06795507
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to hardwired or wireless communication systems; and, more particularly, to a system and method for correctly receiving and decoding transmissions in noisy digital communication environments.
BACKGROUND OF THE INVENTION
Generally, communication channels are limited in transmitter power and spectrum availability. This restricts the amount of information, which may be transmitted over a particular communications environment. High speed data communication services, regardless of various impediments (white gaussian noise or impulsive noise) must fit within the limited bandwidth of spectrum availability provided by the physical medium, or the available frequency spectrum band.
Representative services utilizing wireless networks include telephony, videotelephony, and high-speed data transmission. These services have varying and distinguishable transmission needs which include being in high demand for access, being delay critical, requiring high bandwidth, and/or being intolerant of errors. These different services also have different encoding requirements, different transmission error requirements and different delay requirements. The trade-offs of these different requirements, when the services are integrated into a single cohesive whole, lead to limitations of the network to transmit and receive a large amount of information quickly, correctly and simultaneously.
Further, radio communications are limited in transmitter power and spectrum availability. This also restricts the amount of information which may be transmitted over an air interface. Broadband communication services must fit within the limited narrowband spectrum on an air interface network. Additionally, radio transmission is significantly more error prone than broadband hard-wired networks. This tends to further reduce capacity due to the necessity to transmit and process error control protocols.
It is therefore a goal of digital communications design to maximize the transmission bit rate R and minimize the probability of bit error, or Bit Error Ratio (BER) and required system power S. The minimum bandwidth (BW) required to transmit at rate (R) was given in Nyquist, H., “Certain Topics on Telegraph Transmission Theory,” Trans. Am. Inst. Electr. Eng., Vol. 47, April 1928, p. 617-644, as Rs/2 where Rs is the symbol rate.
A limit on the transmission rate, called the system capacity, is based on the channel BW and the signal to noise ratio (SNR). This limit theorem, also called the Shannon Noisy Channel Coding Theorem, is set forth in Shannon, C. E., “A Mathematical Theory of Communication,” Bell Syst. Tech. J., Vol. 27, 1948, pp.379-423, 623-657, and states that every channel has a channel capacity C which is given by the formula, C=BW log
2
(1+SNR), and that for any rate R<C, there exist codes of rate R
c
which can have an arbitrary small decoding BER.
Turbo Codes
For some time, the digital communications art has sought a coding/decoding algorithm which would reach the Shannon limit. Recently, coding/decoding schemes, called “Turbo Codes,” have been determined to achieve reliable data communication at an SNR which is very close to the Shannon Limit. (Claude Berrou, Alain Glavieux, and Punya Thitimajshima, “Near Shannon Limit Error-Correcting Coding and Decoding: Turbo-Codes”, in Proceedings of ICC'93, Geneve, Switzerland, May 1993, pp. 1064-1070). In fact, Telecommunications Industry Association committee TR45.5 developing IS-95 third generation standards have adopted “Turbo Coding” as the algorithm to be used for data transmission rates higher than 14.4 Kbps.
Generally, there are two known transmission system schemes which implement Turbo Coding. These schemes are known as Parallel Concatenated Coding (PCC) and Serial Concatenated Coding (SCC).
A known implementation of PCC is shown in FIG.
1
. As shown in
FIG. 1
, data is input to the encoder
10
at input
11
. The data is then processed by a first recursive systematic convolutional coder (RSCC)
12
to provide multiple encoder outputs
13
. Each of the set of first encoder outputs
13
provides redundant information representative of the data.
The parallel encoder
10
also sends the data to a second RSCC
14
through interleaver
15
. Interleaver
15
reshuffles the bits of information at input
11
according to a predetermined shuffling sequence and then sends them to second RSCC
14
. By reshuffling the data bits, the second set of outputs
16
from second RSCC
14
are in a different configuration than at the outputs
13
.
In PCC, the various outputs
13
,
16
of the first and second RSCC are also “punctured” or taken from the remainder of the outputs
13
,
16
and selected for transmission. Puncturing outputs is acceptable for transmission purposes because of the redundancy of information which is created within the encoder
10
. Since the signal is being redundantly transmitted from the several outputs
13
,
16
, eliminating some of the parts of the outputs does not degrade signal performance. After the puncturing of the output, encoder
10
has the same rate as a ⅓ rate convolutional encoder. Therefore, there is no additional bandwidth increase.
Another form of Turbo Coding known in the art is Serial Concatenated Coding (SCC).
FIG. 2
shows an illustrated depiction of the architecture used for SCC. As shown in
FIG. 2
, there is a serial cascade of an outer encoder
31
, an interleaver
32
and an inner encoder
33
. The signal to be coded and transmitted is input into the outer encoder
31
. The output of outer encoder
31
is then fed to interleaver
32
where the signal is shuffled in a predetermined manner. The output of interleaver
32
is then sent to the inner encoder
33
for transmission. Most commonly in the art, both the inner and outer encoders use convolutional codes.
There are a few decoding algorithms known in the art which can be used to decode Turbo codes. By way of example only, an iterative decoding algorithm which may be used to decode SCC is described below.
The basic idea of an iterative Turbo decoding algorithm for SCC transmissions is shown in FIG.
3
. As shown in
FIG. 3
, fresh information is generated and fed back to inner decoder
34
or outer decoder
36
in every iteration to update the previous estimates of the intended signals. Iteration stops when the detected coding gain diminishes below a certain threshold, i.e., when all the information is substantially used. In practice, the number of iterations typically varies from about 5 to 12.
In operation, the first iteration produces the conventional non-iterative estimates in the system of FIG.
3
. During the first iteration of the system shown in
FIG. 3
, soft outputs S
o
, consisting of the likelihood (or probability) of the information and code symbols, are fed from a demodulator (not shown) into an Inner Soft-Input Soft-Output (SISO) decoder block
34
. Inner SISO block
34
operates upon logarithmic likelihood ratios as inputs and outputs. The second input I
2
of SISO block
34
is held at zero during-this first iteration. The Inner SISO output O
1
is fed into a de-interleaver
35
and then into inputs I
2
′ of an outer SISO decoder block
36
.
During the following iterations, the outer SISO block
36
output O
2
is fed back through interleaver
37
to the second input I
2
of Inner SISO decoder block
34
until the outer SISO
36
sends the decoded decision output signal along output path O
2
. Refreshed information is generated and fed back to inner decoder
34
or outer decoder
36
in each iteration through blocks
38
,
39
to update the previous estimates of the intended signals.
Trellis Coded Modulation
An important issue in digital communications is the bandwidth BW limitation. It is well known that coding alone provides an effective way to trade off between performance in terms of bit error ratio (BER) and bandwidth BW. If it is not possible to trade off bandwidth BW (i.e., bandwidth BW constrained channels such as the wireless air interface) then a combined cod
Kong Ning
Xin Weizhuang
Goodwin Gruber, L.L.P.
Rourk Christopher J.
Skyworks Solutions Inc.
Tran Khai
LandOfFree
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