Packetized ensemble modem

• US 4,438,511 A
• Filed: 11/10/1980
• Issued: 03/20/1984
• Est. Priority Date: 11/10/1980
• Status: Expired due to Term

• Current Assignee: Telebit Corp. (Cisco Systems, Inc.)
• Original Assignee: Telebit Corp. (Cisco Systems, Inc.)
• Inventors: Baran, Paul
• Primary Examiner(s): Brigance, Gerald L.
• Application Number:
  US06/205,744
• Time in Patent Office: 1,226 Days
• Field of Search: 370/18, 370/70, 370/13, 370/16, 370/17, 370/19, 370/94, 370/60, 370/50
• US Class Current: 370/204
• CPC Class Codes: H04J 1/05 using digital techniques
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/18 Automatic repetition systems, e.g. Van Duuren systems
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 5/006 Quality of the received signal, e.g. BER, SNR, water filling
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26
• CPC Class Codes: Y10S 370/912 Packet communications

Abstract

A high speed digital data modem particularly suited for use on a dial up telephone line is disclosed. For the transmit ensemble, the telephone passband is divided into sixty-four sub-bands each with a carrier located approximately in the center of each sub-band. Each carrier is amplitude and phase modulated in order to encode five (5) bits. One carrier is used as a reference signal for phase and amplitude. The modulated carriers can be changed in data content every epoch. By use of packetization of data, individual amplitude correction, and individual phase correction for each carrier, the high speed modem may achieve up to 12000 bps over a dial up line with a simultaneous 300 bps reverse channel.

Claims

1. A modem for transmitting source information and for receiving destination information in packetized format by means of an ensemble of frequencies through a communication medium having a passband comprising:

a transmit modulator means adapted to impress signals containing said source information upon said communication medium and constructed from

means for generating a plurality of first digital values directly representative of an ensemble of carriers whose frequencies are within said passband,

means for generating second digital values from said first digital values directly representative of modulating said carriers with first unencoded orthogonal signals and encoding said carriers with said information in the form of discrete amplitude and phase deviations, said deviations defining digital data in packets upon said selected ones of said carriers,

means for accurately controlling the duration of said modulating of said carriers for discrete epoch periods,

means for converting said second digital values into analog signals for impression of said analog signals upon said communication medium as modulated carriers at said frequencies of said ensemble of carriers;

a receive demodulator means adapted to extract said destination information from signals impressed upon said communication medium and constructed from

means for generating a plurality of third digital values directly representative of analog signals received through said communication medium, said third digital values being developed by multiplying signals representative of said modulated carriers impressed upon said communication medium by a plurality of signals representative of second orthogonal signals of known amplitude and phase,

means for integrating said third digital values precisely over time to determine frequency and phase of unencoded orthogonal signals substantially idential to said first orthogonal signals and generating therefrom said second orthogonal signals,

means for comparing said third digital signals with fourth digital signals, said fourth digital signals representative of patterns of possible encoded data conveyed by said selected ones of said carriers to decode said destination information, and

means for detecting packets of said data which have been corrupted in transmission; and

means for measuring the transmission characteristics of said communication medium for each of said transmitted carriers constructed from

means for transmitting selected ones of said carriers at a predetermined amplitude level and for a predetermined period,

means for analyzing signal corruption caused by communication medium impairments to received carriers carrying said destination information by comparing received data patterns with known good data patterns, and

means for avoiding use of at least a selected one of said carriers for transmission of data in the event said analyzing means indicates said selected one of said carriers is subject to impairments to said communication medium affecting transmission of data.

2. The packetized ensemble modem of claim 1, wherein said communication medium is a bandlimited telephone line subject to amplitude and phase distortion.

3. The packetized ensemble modem of claim 2, wherein said first unencoded orothogonal signals are a pair of sinusoids that are 90 degrees out of phase.

4. The packetized ensemble modem of claim 1, further comprising:

means for correcting amplitude and phase distortion for each of the received carriers with respect to a reference carrier wherein said reference carrier is one of the plurality of discrete transmitted carriers.

5. The packetized ensemble modem of claim 1 wherein

said carriers are divided into a first group of carriers forming a high speed channel and a second group of carriers forming a low speed reverse channel.

6. The packetized ensemble modem of claim 5 wherein a plurality of input data signals from a plurality of data input sources are multiplexed over a plurality of epoch periods to form error-protected individual units of source information.

7. The packetized ensemble modem of claim 6, wherein

said first group of carriers forming a high speed channel comprises sixty-four (64) carriers,

said second group of carriers forming a low speed reverse channel comprises nine (9) carriers, and

said error-protected data packets each consists of five (5) bits of encoded data per epoch period on each carrier.

8. The packetized ensemble modem of claim 4, further comprising:

means for measuring the phase, amplitude, and noise characteristics of the transmitted carriers corrupted by a first communication medium as received by said receive demodulator,

means for statistically averaging said measured phase, amplitude, and noise characteristics for each of said transmitted carriers over a plurality of epoch periods, and

means for packetizing information constituting said statistically averaged phase, amplitude, and noise characteristics for each of said transmitted carriers and transmitting said packetized information to a remote site over a second communication medium for diagnostic purposes.

9. The packetized ensemble modem of claim 8, wherein

said first communication medium is utilized for the transmission of error-protected data packets, and

said second communication medium is utilized for the transmission of said statistically averaged diagnostic information and voice traffic.

10. In a modem utilized for transmitting source digital information and for receiving destination digital information over a communication medium utilizing a plurality of carriers located within the passband of the communication medium, the improvement comprising:

means for measuring the transmission characteristics of said communication medium constructed from

means for transmitting said source digital information on selected ones of said carriers at a predetermined amplitude level and for a predetermined period,

means for analyzing signal corruption caused by communication medium impairments to received carriers carrying said destination digital information by comparing received data patterns with known good data patterns, and

means for avoiding use of at least a selected one of said carriers for transmission of said source digital information in the event said analyzing means indicates said one of said carriers is subject to impairments to said communication medium affecting transmission of data.