Spectral optimization and joint signaling techniques with...

Details Spectral optimization and joint signaling techniques with... Spectral optimization and joint signaling techniques with...

1998-09-01

2001-09-18

Woo, Stella (Department: 2643)

Telephonic communications

Transmission line conditioning

Interference suppression

C379S416000, C370S201000, C375S296000

Reexamination Certificate

active

06292559

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to electronic communication and, more particularly, to techniques for communicating on communications channels subject to interference such as cross talk and noise.
OUTLINE
Description of the Related Art
1 Communications Background
1.1 Twisted pairs
1.2 Overview of services
1.3 Crosstalk interference
1.3.1 NEXT and FEXT
1.3.2 Notation for self-NEXT and self-FEXT
1.4 Capacity and performance margin
2 Problem Statement
2.1 General statement
2.2 Particular statement for DSLs
2.2.1 HDSL2 service
2.2.2 “GDSL” service
2.2.3 “VDSL2” service
3 Previous Work
3.1 Static PSD Masks and transmit spectra
3.2 Joint signaling techniques
3.3 Multitone modulation
3.4 Summary of previous work
Summary of the Invention
Brief Description of the Drawings
Detailed Description of the Preferred Embodiments
4 New, Optimized Signaling Techniques
4.1 Assumptions, Notation, and Background
4.2 Interference models and simulation conditions
4.3 Signaling schemes
4.4 Optimization: Interference from other services (DSIN-NEXT and DSIN-FEXT)—Solution: EQPSD signaling
4.4.1 Problem statement
4.4.2 Additional assumption
4.4.3 Solution
4.4.4 Examples
4.5 Optimization: Interference from other services (DSIN-NEXT and DSIN-FEXT) plus self-interference (self-NEXT and low self-FEXT)—Solution: EQPSD and FDS signaling
4.5.1 Self-NEXT and self-FEXT rejection using orthogonal signaling
4.5.2 Problem statement
4.5.3 Additional assumptions
4.5.4 Signaling scheme
4.5.5 Solution: One frequency bin
4.5.6 Solution: All frequency bins
4.5.7 Algorithm for optimizing the overall transmit spectrum
4.5.8 Fast, suboptimal solution for the EQPSD to FDS switch-over bin
4.5.9 Flow of the scheme
4.5.10 Grouping of bins and wider subchannels
4.5.11 Examples and results
4.5.12 Spectral compatibility
4.6 Optimization: Interference from other services (DSIN-NEXT and DSIN-FEXT) plus self-interference (self-NEXT and high self-FEXT)—Solution: EQPSD, FDS and multi-line FDS signaling
4.6.1 Self-FEXT and self-NEXT rejection using multi-line FDS
4.6.2 Problem statement
4.6.3 Additional assumptions
4.6.4 Signaling scheme
4.6.5 Solution using EQPSD and FDS signaling: All frequency bins
4.6.6 Switch to multi-line FDS: One frequency bin
4.6.7 Switch to multi-line FDS: All frequency bins
4.6.8 Special case: Performance of 2 lines
4.6.9 Flow of the scheme
4.6.10 Examples and results
4.7 Joint signaling for lines differing in channel, noise, and interference characteristics
4.7.1 Solution for 2 lines: EQPSD and FDS signaling
4.7.2 Solution for M lines: EQPSD and FDS signaling
4.7.3 Solution for 2 lines: EQPSD and multi-line FDS signaling
4.8 Optimizing under a PSD mask constraint: No self-interference
4.8.1 Problem statement
4.8.2 Solution
4.8.3 Examples
4.9 Optimizing under a PSD mask constraint: With self-interference
4.9.1 Problem statement
4.9.2 Solution
4.9.3 Algorithm for constrained optimization of the transmit spectra
4.9.4 Examples and results
4.10 Bridged taps
4.10.1 Optimal transmit spectra
4.10.2 Suboptimal transmit spectra
4.10.3 Examples and discussion
4.11 Optimization: Asymmetrical data-rate channels
4.12 Extensions
4.12.1 More general signaling techniques
4.12.2 More general interferer models
4.12.3 Channel variations
4.12.4 Broadband modulation schemes
4.12.5 Linear power constraints in frequency
4.12.6 CDS signaling under a peak power constraint in frequency
4.12.7 Multi-user detector at central office
5 Summary of Contributions
References
Glossary
Notation
DESCRIPTION OF THE RELATED ART
1 Communications Background
1.1 Twisted pair telephone lines
Telephone service is provided to most businesses and homes via a pair of copper wires (a “twisted pair”). A telephone cable contains many twisted pairs: 25 twisted pairs are grouped in close proximity into 2 “binder groups,” and several binder groups are packed together to form a cable. The two terminations of a telephone cable are at the user (subscriber) end and at the telephone company (central office, CO) end. We will use the terms “twisted pair,” “line,” and “subscriber loop” interchangeably herein as one example of a communications channel.
Voice telephony uses only the first 4 kHz of bandwidth available on the lines. However, one can modulate data to over 1 MHz with significant bit rates. Only recently have schemes been developed to exploit the additional bandwidth of the telephone channel. A plot of the frequency response of a typical telephone channel is given in FIG.
1
.
1.2 Overview of services
In the past few years, a number of services have begun to crowd the bandwidth of the telephone channel. Some of the important services are:
POTS—“Plain Old Telephone Service.” This is the basic telephone service carrying voice traffic in the 0-4 kHz bandwidth. Conventional analog modems also use the same bandwidth.
ISDN—Integrated Services Digital Network. This service allows end-to-end digital connectivity at bit rates of up to 128 kbps (kilo-bits-per-second).
T1—Transmission 1. This is a physical transmission standard for twisted pairs that uses 24 multiplexed channels (each at 64 kbps) to give a total bit rate of 1.544 Mbps (Mega-bits-per-second). It uses costly repeaters.
HDSL—High bit-rate Digital Subscriber Line. This is a full-duplex (two-way) T1-like (1.544 Mbps) signal transmission service using only two twisted pairs and no repeaters.
ADSL—Asymmetric Digital Subscriber Line. Over one twisted pair, this service provides a high-speed (on the order of 6 Mbps) downstream (from central office (CO) to subscriber) channel to each user and a low-speed (on the order of 640 kbps) upstream (from subscriber to the central office) channel. This service preserves the POTS service over a single twisted pair.
VDSL—Very high bit-rate DSL. This yet-to-be-standardized service will provide a very high speed (on the order of 25 Mbps) downstream channel to subscribers and a lower speed upstream channel to the central office over a single twisted pair less than 3 to 6 kft long. Further, it will preserve the POTS service.
HDSL2 —High bit-rate Digital Subscriber Line 2. This soon-to-be-standardized service will provide full-duplex 1.544 Mbps signal transmission service in both directions (full duplex) over a single twisted pair (<18 kft long) without repeaters.
“GDSL”—General Digital Subscriber Line. This hypothetical service would (for illustration purposes) carry 25 Mbps full-duplex data rate over a single twisted pair (see Sections 2.2.2 and 4.6.10).
“VDSL2”—Very high bit-rate DSL Line 2. This hypothetical service would (for illustration purposes) carry 12.4 Mbps fall-duplex data rate over a single twisted pair less than 3 to 6 kft long (see Sections 2.2.3 and 4.6.10).
Currently, all the above mentioned services have an ANSI standard except for VDSL, HDSL2, “GDSL” and “VDSL2”.
1.3 Crosstalk interference
1.3.1 NEXT and FEXT
Due to the close proximity of the lines within a binder, there is considerable amount of crosstalk interference between different neighboring telephone lines. Physically, there are two types of interference (see in FIG.
2
):
Near-end crosstalk (NEXT): Interference between neighboring lines that arises when signals are transmitted in opposite directions. If the neighboring lines carry the same type of service then the interference is called self-NEXT; otherwise, we will refer to it as different-service NEXT.
Far-end crosstalk (FEXT): Interference between neighboring lines that arises when signals are transmitted in the same direction. If the neighboring lines carry the same type of service then the interference is called self-FEXT; otherwise, we will refer to it as different-service FEXT.
FIG. 3
shows that crosstalk interference can be modeled as additive interference. Since neighboring lines may carry either the same or a different flavor of service, there are three categories of interference (see FIG.
3
):
1. Self-interference (self-NEXT and self-FEXT) between lines carrying the same service.
2. Interference into a channel carrying service A from other lines carrying services other than A (DSIN-NEXT and DSIN-FEXT).
3. Interference from

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