A pilot phase tracking loop for an OFDM receiver including a phase rotator receiving an incoming signal, a fast Fourier transform coupled to a phase rotator output, and a pilot phase error metric including a discrete Fourier transform portion coupled to the phase rotator output. The pilot phase error metric determines a phase error estimate associated with a received OFDM symbol, e.g., a data symbol, from the phase rotator output. A loop filter is coupled to the pilot phase error metric output and an oscillator is coupled to the loop filter output. The oscillator output is coupled to the phase rotator to adjust the phase of subsequent OFDM symbols of the incoming signal. Phase noise introduced by a radio portion of the OFDM receiver and OFDM transmitter is reduced by the baseband portion of the OFDM receiver improving OFDM signal tracking under poor SNR conditions.

Ofdm pilot tone tracking for wireless lan

A modem for use in Digital Subscriber Line communications transmits and receives data over the local subscriber loop in common with voice information over the loop, while avoiding the need for voice/data splitters. The modem responds to disruptions associated with “disturbance events” such as on-hook to off-hook transitions and the like by rapidly switching between pre-stored channel parameter control sets defining communications over the loop under varying conditions. In addition to changing parameter control sets responsive to a disturbance event, the modem may also change transmission power levels and other system parameters such as frequency domain equalizer characteristics. Further, provisions are made for reduced bandwidth communications under selected conditions.

Splitterless multicarrier modem

An OFDM communication channel using both frequency and time diversity (Fig. 1). The OFDM communication channel is used for wireless networks. It further includes a system for performing an ordinary OFDM such as DVB-H/T, and using lower coding rate techniques and interleaving for achieving extra time diversity, frequency diversity, hybrid frequency time diversity or further frequency, time and space diversity.

Ofdm communication channel

In a wireless packet switching telecommunications network, voice services are provided by having a compressor/decompressor in each mobile station to provide each voice packet with a compressed header. Voice data and signalling data are sent separately and in different data formats to the air interface. The compressed header may be an M bit and a cyclically reset timeclick_number, which is decompressed by use of a wallclock which counts reset cycles to reinstate the voice packet headers. Alternatively, RTP agents are provided at the compression and decompression points, and voice packets are sent without headers over a 'high quality' network such as a frame relay or ATM network. Compression state of a voice packet header can be established by sending call set-up information over an out-of-band channel between compression points in a mobile station and in the network.

Method and apparatus for telecommunications using internet protocol

Data is distributed among the channels of an asynchronous data subscriber loop (ADSL) communications system in accordance with an adaptive algorithm which from time to time measures the signal to noise ratio of the various channels and finds a margin for each channel dependent on achievement (where possible) of a given bit error rate and a desired data transmission rate. The margin distribution is achieved by augmenting the constellation signal to noise ratio to enhance computational efficiency and allow redetermination of bit allocation tables during transmission as necessary. Pairs of bit allocation tables are maintained at the transmitter and receiver and one table of each pair at the transmitter and receiver is updated while the other pair is in use for controlling communication.

Adaptive allocation for variable bandwidth multicarrier communication

A modem ( 55 ) including receive circuitry ( 30 ) implemented by way of a digital signal processor ( 32, 32′ ) is disclosed. The receive circuitry ( 30 ) operates according to a receive clock (CLK r ) that is based upon the output of a free run oscillator ( 50 ). An incoming frequency multiplexed signal (f(t)) is sampled by an analog-to-digital converter ( 31 ) and demodulated by way of a Fast Fourier Transform function ( 36 ). After such demodulation, a phase rotation function ( 40 ) applies a phase shift to the demodulated signal corresponding to an estimated phase offset (τ) between the receive clock (CLK r ) and a pilot signal (P) transmitted by the transmitting modem; a finite impulse response filter function ( 42 ) applies a digital filter to the demodulated signal to correct for phase error based upon an estimated frequency offset (Δ). According to another disclosed embodiment, a pre-emphasis FIR filter function ( 52 ) and a pre-emphasis phase rotation function ( 54 ) are applied to an upstream singal, based upon the estimated phase offset (η) and frequency offset (Δ).

Phase and frequency offset compensation in a telecommunications receiver

A modem that operates selectively in the voice-band frequency band and at higher frequency bands is provided. This modem supports multiple line codes,like DMT and CAP. The modem uses a Digital Signal Processor (DSP), so that different existing ADSL line codes, such as Discrete MultiTone (DMT) and Carrierless AM/PM (CAP), can be implemented on the same hardware platform. The modem negotiates in real-time, for a desired line transmission rate to accommodate line condition and service-cost requirement. The line code and rate negotiation process may be implemented at the beginning of each communication session through the exchange of tones between the modems. A four-step MDSL modem initialization process is provided for line code and rate capatibility. A new synchronization startup procedure for CAP based MDSL modems is provided. The handshake protocol and receiver algorithm allow reliable modem synchronization over severely amplitude distorted channels such as standard telephone twisted-pair wire. The algorithm makes use of a short length sequence to train a synchronizing equalizer at the receiver. After training to this sequence, a matched filter or correlator is used to detect the inverted sync sequence. The detection of the inverted sequence signals the start of the normal reference training of the CAP demodulation equalizers. The MDSL line connection management process provides a simple, efficient, and flexible interface to manage the line connection between MDSL-C (MDSL in Central Office site) and MDSL-R (MDSL ion resident site) in the telecommunication Wide Area Networking environment. An internal state machine in an MDSL modem records and monitors the line status and notifies the state change to the other MDSL and also the host processor. The protocol used for exchanging line connection management messages is a simplified Link Control Protocol (LCP) for MDSL. In a DMT system a transmitter filter is provided to reduce the length of effective channel impulse response. The implementation of the filter combines time domain convolution and frequency domain multiplication to reduce the needed computation power. The algorithm and corresponding training sequence to train the transmitter filter are provided. The filter coefficients update may occur through a feedback channel.

Multimode modem, and protocols therefor

A modem (55) including receive circuitry (30) implemented by way of a digital signal processor (32; 32') is disclosed. The receive circuitry (30) operates according to a receive clock (CLKr) that is based upon the output of a free run oscillator (50). An incoming frequency multiplexed signal (f(t)) is sampled by an analog-to-digital converter (31) and demodulated by way of a Fast Fourier Transform function (36). After such demodulation, a phase rotation function (40) applies a phase shift to the demodulated signal corresponding to an estimated phase offset (τ) between the receive clock (CLKr) and a pilot signal (P) transmitted by the transmitting modem; a finite impulse response filter function (42) applies a digital filter to the demodulated signal to correct for phase error based upon an estimated frequency offset (Δ). According to another disclosed embodiment, a pre-emphasis FIR filter function (52) and a pre-emphasis phase rotation function (54) are applied to an upstream signal, based upon the estimated phase offset (τ) and frequency offset (Δ).

Sampling clock correction in a multicarrier receiver

PROBLEM TO BE SOLVED: To attain a high transmission rate for data while using an existing twisted pair. SOLUTION: A MODEM operated selectively in a voice frequency band and at a higher frequency band than it is provided. The MODEM supports lots of channel codes such as the DMT and the CAP. This MODEM uses a digital signal processor(DSP) so as to execute a different existing ADSL channel code on a same hardware platform, e.g. a discrete multi-tone(DMT) and a non- carrier AM/PM (CAP). The MODEM decides a desired channel transmission rate in real time so as to be in matching with a channel state and a service cost condition.

Method and device for generating frame of digital data to be sent through channel

Korrektur des Abtasttaktes in einem Mehrträgerempfänger

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