3com Corporation

Texas Instruments Corporation

Richard G C Williams

A Joseph Mueller

John R Rosenlof

Vlad Mitlin

Anuj Batra

Kofi Dankwa Anim-Appiah

Srikanth Gummadi

Andrew L Norrell

Giuseppe Surace

Chris Heegard

Yaqi Cheng

Dale M Walsh

Tim Murphy

William Kurt Dobson

Peter Murphy

George F Landsburg

Jeff E Taarud

G Layne Lisenbee

A data receiver has a clock recovery and data sampling circuit. This has a fixed local oscillator for timing the data samples. A phase interpolator adjusts the phase of the clock signal in response to an early late detector which samples the waveform at the expected position of the edges. A further correction to the sampling position is made in response to the recent history of the data received. The correction is modelled on predictable jitter, for example, that in a transmitter caused by changes in data causing the supply voltage to drop.

Use of data decisions for temporal placement of samplers

A communication system disclosed herein includes a channel quality estimation module that determines the channel quality metric utilizing the preamble portion of the packet only. Data, in such a communication system, is transmitted in the form of a packet over a data channel during a packet transmission, wherein each data channel includes several subchannels. The system includes a receiver having at least a baseband processor. The baseband processor couples to receive each baseband sample signal. Specifically, the baseband processor calculates the gain estimation of the each subchannel and generates a channel quality metric for each subchannel that is derived by deinterleaving the sequence of gain estimation magnitudes, convolving the deinterleaved sequence of gain estimation magnitudes with a short window index, and detecting the number of times the convolution falls beneath a predetermined threshold.

Method and apparatus for channel quality metric generation within a packet-based multicarrier modulation communication system

A communication system includes a receiver having a variable gain module and a baseband processor. The baseband processor measures the power of the signal received and derives a variable gain control setting that is inversely proportional to the power of that signal and sends the variable gain control setting to the variable gain module. The baseband processor generates a channel quality metric that is equivalent to the normalized geometric mean of the squared magnitudes of the gain estimation, divided by the total noise-plus-interference power.

System and method for enabling the low power detection of a transmitted sequence. A preferred embodiment comprises the replacement of a portion of a preamble (after the application of any needed scrambling) with an expected sequence field (such as the expected sequence field). The expected sequence field may contain a sequence of values known at a receiver or a periodic sequence. The addition of the expected sequence field does not affect the length of the preamble and is compatible with existing receivers. The detection of the expected sequence field may be performed with analog circuitry, allowing receivers to place digital circuitry to sleep and reduce power

Enhanced preamble to enable low power detection

A separated synchronizing scrambler/descrambler pair that removes the possibility of catastrophic error due to improper transmission of initial condition information without disrupting the OFDM modulation scheme of a system that includes error-correction coding circuitry and replay variation. A transmitting device within the pair includes a first and a second data scrambler wherein the first data scrambler couples to receive the incoming data stream and filters the incoming data stream to provide a first filtered signal using a key signal. The second data scrambler, having an initial condition, couples to receive the first filtered signal and converts it into a scrambled signal using a scrambling seed. The second data scrambler comprises a random series generator for generating the scrambling seed to convert the first filtered signal into a scrambled signal. The scrambled signal is transmitted to the receiving device. A receiving device within the pair includes a first and a second data descrambler coupled together. The first data descrambler, having an initial condition equivalent to that of the second data scrambler, couples to receive the transmitted scrambled input data stream to convert it into a descrambled signal using a descrambling seed equivalent to the scrambling seed. The first data descrambler includes a random series generator for generating the descrambling seed. The second data descrambler couples to receive the descrambled signal and filters it to provide a filtered descrambled signal using a feedforward filter and a key signal. The feedforward filter is structured similar to the feedback filter.

Separate self-synchronizing packet-based scrambler having replay variation

A method for estimating carrier frequency offset (CFO) and sampling frequency offset (SFO) in an Orthogonal Frequency Division Multiplexing (OFDM) system having a plurality of pilot tones. The absolute phase angle for each pilot tone is measured, and estimates of the CFO and the SFO are derived using a weighted least-squares methodology. More particularly, the phase of each pilot tone is measured for a number (n) of symbol times; for each of the pilot tones, the slope of a phase angle change from symbol time to symbol time is estimated using a best least-squares fit of the measured phases to a straight line; and a weighted least-squares best-fit straight line is determined to find an estimated phase angle differential value (&#x3b1;(i)) for each pilot tone; wherein a slope of the best-fit straight line yields an estimate of the SFO, and an intercept with the best-fit straight line yields an estimate of the CFO. The plurality of pilot tones may have frequencies which are symmetrically disposed about a reference frequency, and there may be four pilot tones. The OFDM communications system is suitably a wireless LAN (WLAN) implementing a standard such as IEEE 802.11a or HiperLAN/2. Corresponding apparatus is also described.

Estimating frequency offsets using pilot tones in an OFDM system

A method and apparatus determines an uncoded bit error rate pbased on a target symbol error rate &#x3b5;. The uncoded bit error rate pis determined based on a weighted series expansion of the target symbol error rate &#x3b5;, comprising weights W that are a function of a maximum number of symbol errors that can be corrected t and a number of symbols in an information field K. The maximum number of symbol errors t and the number of symbols in the information field K is selected such that the uncoded bit error rate pthat produces a symbol error rate that is less than or equal to the target symbol error rate &#x3b5;is largest.

Performance evaluation of multicarrier channels

In one embodiment, a method and apparatus increases a bit load of a multicarrier system comprising a channel having a plurality of subchannels. A bit load is determined for at least one subchannel based on a target symbol error rate &#x3b5;a maximum number of symbol errors that can be corrected t, a number of symbols in an information field K, and a maximum number of transmissions k, and a number of bits per subchannel. The maximum number of symbol errors t, the number of symbols in the information field K and the maximum number of transmissions k, is selected such that a net coding gain is increased. In another embodiment, a method determines data flow for a channel having a plurality of subchannels in a multi-carrier system.

Performance evaluation of multicarrier channels with forward error correction and automatic retransmission request

A methodis provided to mitigate DC offset in a sign bit correlator associated with a packet detection circuit. The input sign pattern is monitored; and if a long run of the same sign is seen, a sign bit is replaced with a bit generated using a desired pseudorandom noise (PN) sequence. This ensures that the correlator only reacts substantially to correlations that are not due to DC offset.

Method for mitigating DC offset in a sign bit correlator

A differential encoder is designed to correct for any phase invariance. Without differential encoding defined for the V.92 upstream, undetectable errors are possible in a modem due to an inversion in the upstream channel. Immunity to channel inversions is provided by differentially encoding a combined preceding and modulus conversion system. A frame of a constellations is attributed a sign and the frame and the sign are differentially encoded. The frame and the sign are differentially decoded after the multiple modulus decoder, ensuring phase shift immunity.

Method of differential encoding a precoded multiple modulus encoder

A system and method for providing a local area network utilizing discrete multitone transceivers includes at least two discrete multitone transceivers each of which may be capable of communicating with the central office and with other discrete multitone transceivers in communication with the local area network. The local area network utilizes a set of carriers coordinated between the first discrete multitone transceiver and the second discrete multitone transceiver providing a communication link between the first discrete multitone transceiver and the second discrete multitone transceiver.

System and method for providing a local area network utilizing remote transceivers

The present invention includes alternative methods for selecting forward error correction parameters to be used in multi channel communications. Method embodying aspects of the present invention may include acquiring signal to noise ratio data for a set of communications channels, counting, estimating or identifying channels to carry data, computing an average signal to noise ratio for channels used and selecting set(s) of FEC parameters. It may predicting net SNR gains and storing these predictions as splines or in interpolation tables. This invention is specifically applicable to Reed-Solomon encoding for FEC and selecting the Reed-Solomon parameters S and R/S. Symbol sets, represented by S may consist of dmt symbols or of data carried by multiple channels in one transmission interval. The computations for selecting parameters may include adjusting the average signal to noise ratio by a safety margin. The selected sets of parameters may be chosen from sets identified by a sending terminal and may be forwarded from a receiving terminal to a sending terminal.

Method of selecting initialization parameters for multi-channel data communication with forward error correction

The subject invention defines the details of packet based DSL modulation. The invention claims a method for minimizing crosstalk generation by specifying a duty cycle for bursted carrier data traffic and a method of providing opportunistic echo canceller training. In this way the present invention minimizes power and interference while maximizing the peak capacity of a transceiver used in ADSL communication systems.

Packet modulation for DSL

A system and method for a handshake protocol for digital subscriber line (DSL) and similar telecommunication systems that makes beneficial use of aliasing to select and decode signaling tones. In particular, the invention carefully selects signaling tones at frequencies such that higher frequency tones would alias down and coincide with specific base tones after sub-sampling. Thus, rather than filtering out higher frequencies to avoid aliasing, aliasing is exploited to use these higher frequencies. This technique would allow a receiver to detect and decode the higher frequency tones at lower frequency tone locations or bands. A related innovation is a band set, which includes one or more tones within a particular frequency band, where typically each tone in a band set corresponds to a different tone set. Exploiting the effects of aliasing eliminates the need to search for compatible spectrum, simplifies receiver design, provides flexibility, scalability and future-proofing, and allows handshaking sessions to be established across mutually exclusive spectrums. The invention is particularly useful for DSL systems, and in particular is well suited for the proposed G.hs standard.

Controlled aliasing to simplify service selection

A method of transmitting a quite, or zero, signal in a PCM communication system. The zero signal is specified universally in ordered set terms for either &mgr;-Law or A-Law PCM systems, which has minimal energy in the A-Law system, and contains no energy within the &mgr;-Law system. The signal is preferably specified as a repetition of six intervals (or multiple thereof) because the DTN can modify PCM codes on a six interval period by the robbed-bit signaling mechanism. The zero signal may be used to detect network elements that produce single-signed zero outputs from zero inputs of either sign. In addition, by examination of the zero signal the receiver may determine whether the channel includes an analog link or connection.

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San Diego, CA, United States of America

Richard G C Williams