Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
1999-03-24
2002-11-12
Pham, Chi (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S341000
Reexamination Certificate
active
06480552
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method for generating and calculating reliability information with the use of a symbol detector used in a receiver for a digital communication system.
2. Description of the Related Art
Digital telecommunication systems convey digital information (i.e., bits or groups of bits) over various types of communication channels such as air, coaxial cables, telephone lines, fiber optic lines or any other well known medium through which communication signals propagate. The digital information is transmitted and received with the use of well known standard transmitter and receiver equipment.
FIG. 1
depicts a model of a typical digital communication system comprising a transmitter connected to a receiver via a communication channel. The transmitter comprises convolutional encoder
102
coupled to Interleaver
104
which is coupled to modulator
106
. The input signal b
i
is typically a string or a group of bits (e.g., 0,1) arranged in any well known format. The digital bits represent any type of signals (digital or analog) originating from any well known communication equipment. For example, the input signal can represent digitized voice, digitized video signal or digital signals from a personal computer (PC) or computer system. Although not shown, it should be understood that the transmitter also comprises circuitry (e.g., Analog to Digital Converter) that converts analog signals to bits. Further, the transmitter comprises well known radio or other transmission circuitry configured to transmit digitally modulated signals which appear at the output of modulator
106
.
Modulator
106
is designed to digitally modulate signals with the use of well known spectrally efficient modulation techniques such as Phase Shift Keying (PSK) or Differential Phase Shift Keying (DPSK). Generally, modulator
106
is an M-PSK or M-DPSK modulator where M represents the total number of different groupings of bits that can be transmitted by a digital modulator. For example for M=8, each grouping of bits contains N bits where N=log
2
M. Thus, for M=8, N is equal to 3. The modulation process maps the incoming bits d
i
(i=0, . . . , N
d−
1; where N
d
is the number of bits in the sequence) into symbols (e.g., an M-PSK signal); one well known mapping technique is called Gray mapping which is shown in
FIG. 2
for M=2, 4, 8. The symbols x
i
(i=0, . . . , N
k
−1; where N
k
is the number of symbols in the sequence) are simply digital signals modulated in conformance with a particular modulation scheme (e.g., PSK). M-PSK and M-DPSK are examples of constant envelope modulation techniques because the maximum amplitude values of signals used to generate the symbols are relatively constant. When the maximum amplitude values of the signals used to generate the symbols are not constant, the modulation is referred herein as nonconstant envelope modulation. The output of modulator
106
(i.e., symbols x
i
) is then transmitted through channel
108
with the use of the aforementioned radio transmission circuitry. The incoming bits to modulator
106
are the output of interleaver
104
whose input signal is c
i
(i=0, . . . , N
c
−1; where N
c,
is the number of bits in the sequence). The signal c
i
is a string or a grouping of bits, each of which is commonly referred to as a codeword, appearing at the output of convolutional encoder
102
.
Convolutional encoder
102
is a well known bit processing device and/or function which, in essence, adds bits to the incoming bit stream b
i
(i=0, . . . , N
b
−1; where N
b
is the number of bits in the sequence) to introduce redundancy in the incoming bits stream thus allowing for error correction at the receiver. The convolutionally encoded bits are represented by bit stream c
i
which is interleaved by interleaver
104
. Interleaver
104
is also a well known bit processing device and/or function that alters the time order of the bits represented by c
i
thus introducing time diversity in a bit stream without adding bits to the bit stream. Although convolutional encoder
102
, interleaver
104
and modulator
106
are described and depicted as separate devices, they can also be different parts of a signal processing and/or computer based system.
The receiver of the communication system model comprises a device hereinafter be referred to as Soft Output Detector (SOD)
110
. The receiver further comprises Deinterleaver
112
and another device hereinafter referred to as Soft Input Decoder (SID)
114
. SOD
110
is coupled to Deinterleaver
112
which is coupled to SID
114
. It will be readily understood that the receiver typically comprises a plurality of receiving devices each of which is configured to receive a separate signal. For example the receiver shown in
FIG. 1
comprises N
a
receiving devices (not shown) where N
a
is an integer equal to or greater than 1. In the case where the receiving device is an array of N
a
antennae, the communication system modeled in
FIG. 1
may be, for example, a mobile communication system (i.e., a wireless communication system). In a mobile (wireless) communication system (and other communication systems) each antenna receives signals located in a certain frequency band. The received signal is downconverted (i.e., frequency content of the signal is changed to lower frequencies) and applied to a matched filter. The filtered signal is sampled at a rate greater than or equal to 1/T where T is a period of time that represents a signaling interval (i.e., the amount of time between transmission of two consecutive symbols). The samples (i.e., sampled received signals,y
i
) are fed to SOD
110
. Further, well known receiver circuitry (e.g., amplifiers, filters), which are not shown, are also used to receive the plurality of different signals conveyed over channel
108
. For the sake of simplicity and ease of illustration, the N
a
antennae and associated receiver circuitry are not shown. It will be readily understood that the receiver may be implemented with any well known receiving devices (other than antennae) that allow it to receive a plurality of separate signals. However, the receiving devices are hereinafter referred to as antennae simply for ease of discussion only. SOD
110
is a device that generates reliability information (&OHgr;
i
) from the samples y
i.
The reliability information (or soft outputs) generated by SOD
110
represents a probability that the received signal is a particular group of bits from the set of bits defined by modulator
106
and examples of which are shown in
FIG. 2
, or the probability of each single bit within each transmitted symbol. It is important to note that the reliability information does not represent the actual transmitted signal but it provides an indication of the most likely signal that was transmitted. The output of SOD
110
(i.e., &OHgr;
i
) is applied to Deinterleaver
112
. Deinterleaver
112
performs the inverse operation of Interleaver
104
in that the signals &OHgr;
i
are rearranged in their proper time order. The output of Deinterleaver
112
(&OHgr;
i
′) is applied to Soft Input Decoder
114
(SID). SID
114
performs a decoding operation that serves to decode the output of Deinterleaver
112
into a stream of bits represented by b′
i
. Assuming the transmitter has a convolutional encoder, one example of a corresponding decoding operation is the Soft Input Viterbi Decoder which applies the well known Viterbi Decoding algorithm; G. D. Forney,
“The Viterbi Algorithm,” Proc. IEEE, March
1973, pp. 268-278.
Samples y
i
represent the transmitted symbols x
i
after they have propagated through channel
108
. Channel
108
has well known characteristics (e.g., amplitude response, phase response, impulse response) that alter the transmitted symbols. As is well known in communication theory, the channel is a source of distortions, viz., multiplicative distortion, (e.g., phase jitter, amplitude degradation, f
Lucent Technologies - Inc.
Mendelsohn and Associates PC
Phu Phuong
LandOfFree
Soft output metrics generation for symbol detectors does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Soft output metrics generation for symbol detectors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Soft output metrics generation for symbol detectors will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2918611