Source: http://www.google.com/patents/US20070109995?dq=6275268
Timestamp: 2015-09-04 21:36:59
Document Index: 788456760

Matched Legal Cases: ['Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60']

Patent US20070109995 - Compensating for noise in a wireless communication system - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA number of features for enhancing the performance of a communication system, in which data is transmitted between a base station and a plurality of subscriber stations located different distances from the base station, are presented. The power transmission level, slot timing, and equalization of the...http://www.google.com/patents/US20070109995?utm_source=gb-gplus-sharePatent US20070109995 - Compensating for noise in a wireless communication systemAdvanced Patent SearchPublication numberUS20070109995 A1Publication typeApplicationApplication numberUS 11/584,676Publication dateMay 17, 2007Filing dateOct 23, 2006Priority dateOct 30, 1998Also published asUS7103065, US7512154, US7519082, US7821954, US7843847, US8483080, US20060088056, US20070036176, US20070086484, US20110026423, US20130294377Publication number11584676, 584676, US 2007/0109995 A1, US 2007/109995 A1, US 20070109995 A1, US 20070109995A1, US 2007109995 A1, US 2007109995A1, US-A1-20070109995, US-A1-2007109995, US2007/0109995A1, US2007/109995A1, US20070109995 A1, US20070109995A1, US2007109995 A1, US2007109995A1InventorsThomas Quigley, Jonathan Min, Lisa Denney, Henry Samueli, Sean Nazareth, Feng Chen, Fang Lu, Christopher JonesOriginal AssigneeBroadcom CorporationExport CitationBiBTeX, EndNote, RefManReferenced by (32), Classifications (43), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetCompensating for noise in a wireless communication system
US 20070109995 A1Abstract
A number of features for enhancing the performance of a communication system, in which data is transmitted between a base station and a plurality of subscriber stations located different distances from the base station, are presented. The power transmission level, slot timing, and equalization of the subscriber stations are set by a ranging process. Data is transmitted by the subscriber stations in fragmented form. Various measures are taken to make transmission from the subscriber stations robust. The uplink data transmission is controlled to permit multiple access from the subscriber stations. Images(83) Claims(24)
1. A base station that can receive signal bursts transmitted on an uplink channel of a wireless communication system, the base station comprising: a demodulator for receiving the signal bursts on the uplink channel; a media access controller (MAC) that generates for downlink transmission MAP messages that assign time slots in which subscriber stations may transmit signal bursts on the uplink channel, the MAP messages including idle slots that are assigned to no subscriber stations; a transmitter that transmits the MAP messages with the idle slots to the subscriber stations; and an adaptive notch filter connected to the demodulator, wherein coefficients of the adaptive notch filter are adjusted to suppress noise on the uplink channel sensed during the idle slots. 2. The base station of claim 1, further comprising a decision feedback equalizer coupled to the demodulator and the notch filter, the decision feedback equalizer having a feedback filter using the adjusted coefficients of the adaptive notch filter to compensate for distortion introduced by the adaptive notch filter. 3. The base station of claim 2, wherein the decision feedback equalizer has a feedforward filter for establishing pre-equalization coefficients. 4. The base station of claim 3, wherein the demodulator converts the signal bursts to binary data, the base station further comprising a signal path for carrying the binary data from the demodulator to the MAC, the notch filter and the decision feedback equalizer being in the signal path. 5. The base station of claim 4, wherein the signal path carries both the binary data and the pre-equalization coefficients to the MAC in band such that the coefficients are appended to the binary data. 6. The base station of claim 5, wherein the pre-equalization coefficients do not reflect noise received by the demodulator, the base station further comprising an uplink transmitter for transmitting the pre-equalization coefficients established by the feedforward filter. 7. The base station of claim 6, wherein the uplink transmitter is connected to the MAC to transmit the pre-equalization coefficients established by the feed forward filter. 8. A base station that can receive a signal transmitted in a wireless communication system on an uplink channel, the base station comprising: a demodulator; a notch filter connected to the demodulator, the notch filter having coefficients that are adjustable to cancel noise applied to the demodulator; a media access controller (MAC) that processes binary data and generates for downlink transmission MAP messages that assign time slots in which subscriber stations may transmit signal bursts on the uplink channel; and a decision feedback equalizer coupled to the demodulator, the decision feedback equalizer including a feedforward filter for establishing pre-equalization coefficients. 9. The base station of claim 8, wherein both binary data and pre-equalization coefficients are provided to the MAC in band such that the coefficients are appended to the binary data. 10. The base station of claim 9, wherein the pre-equalization coefficients do not reflect noise applied to the demodulator, the base station further comprising an uplink transmitter connected to the MAC to transmit the pre-equalization coefficients established by the feedforward filter. 11. A base station comprising: means for transmitting on a downlink channel to a plurality of subscriber stations MAP messages that assign time slots in which subscriber stations may transmit signal bursts on an uplink channel, the MAP messages including idle slots that are assigned to no subscriber stations; means for monitoring conditions on the uplink channel during the idle slots; means for compensating for the monitored conditions on the uplink channel; and means for receiving signal bursts on the uplink channel in response to such compensation. 12. The base station of claim 11, wherein the means for monitoring is configured to sense noise on the uplink channel during the idle slots. 13. The base station of claim 12, wherein the means for compensating is configured to adjust coefficients of a notch filter to compensate for the sensed noise on the uplink channel during the idle slots. 14. The base station of claim 13, wherein the means for compensating is further configured to adjust a feedback filter of a decision feedback filter in series with the notch filter to have the same coefficients as the notch filter to compensate for its distortion. 15. The base station of claim 14, wherein the means for compensating is further configured to adjust coefficients of a feedforward filter of the decision feedback filter based on a ranging signal of a subscriber station to compensate for intersymbol interference on the uplink channel; and wherein the means for transmitting is configured to transmit the adjusted coefficients on a downlink channel to the subscriber station for the purpose of pre-equalization. 16. The base station of claim 15, wherein the means for transmitting is configured to transmit the MAP messages and the adjusted coefficients on the same channel. 17. A base station comprising: means for compensating for noise on an uplink channel; means for receiving on the compensated uplink channel a ranging signal from a subscriber station of a plurality of subscriber stations; means for adjusting filter coefficients to compensate for intersymbol interference on the uplink channel based on the received ranging signal; and means for transmitting the adjusted coefficients on a downlink channel to the subscriber station for the purpose of pre-equalization of the uplink channel. 18. The base station of claim 17, wherein the means for adjusting is configured to adjust coefficients of a feedforward filter of a decision feedback filter. 19. The base station of claim 18, wherein the means for compensating is configured to adjust the coefficients of a notch filter in series with the decision feedback filter. 20. The base station of claim 19, wherein the means for compensating is further configured to adjust a feedback filter of the decision feedback filter to have the same coefficients as the notch filter to compensate for its distortion. 21. The base station of claim 20, wherein the means for transmitting is configured to transmit on a downlink channel to the subscriber stations MAP messages that assign time slots in which subscriber stations may transmit signal bursts on the uplink channel. 22. The base station of claim 21, wherein the means for transmitting is configured to transmit the MAP messages and the adjusted coefficients on the same channel. 23. In a wireless communication system, a subscriber station comprising: a transmitter to transmit a ranging signal to a base station; a receiver to receive pre-equalization coefficients from the base station, wherein the pre-equalization coefficients are based on the ranging signal; and a transmit equalizer to compensate for noise associated with the subscriber station based on the pre-equalization coefficients. 24. The subscriber station of claim 23, wherein the pre-equalization coefficients represent frequency shaping necessary to compensate for the noise that is unique to the subscriber station.
CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. patent application Ser. No. 11/292,098, filed Dec. 2, 2005, which is a continuation of U.S. patent application Ser. No. 09/714,713, filed Nov. 16, 2000, now U.S. Pat. No. 7,103,065, which is a continuation of U.S. patent application Ser. No. 09/574,558, filed May 19, 2000, now U.S. Pat. No. 6,650,624, which is a continuation-in-part of U.S. patent application Ser. No. 09/430,821, filed Oct. 29, 1999, which claims the benefit of U.S. Provisional Patent Application No. 60/106,264, filed Oct. 30, 1998, U.S. Provisional Patent Application No. 60/106,427, filed Oct. 30, 1998, U.S. Provisional Patent Application No. 60/106,438, filed Oct. 30, 1998, U.S. Provisional Patent Application No. 60/106,439, filed Oct. 30, 1998, U.S. Provisional Patent Application No. 60/106,440, filed Oct. 30, 1998, and U.S. Provisional Patent Application No. 60/106,441, filed Oct. 30, 1998, all of which are incorporated herein by reference in their entireties.
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to communication systems, and more specifically to noise compensation in a wireless communication system. 2. Background Art The desired solution for high speed data communications appears to be cable modem. Cable modem is capable of providing data rates as high as 56 Mbps, and is thus suitable for high speed file transfer, video teleconferencing and pay-per-view television. Further, cable modems may simultaneously provide high speed Internet access, digital television (such as pay-per-view) and digital telephony. Although cable modems are used in a shared access system, wherein a plurality of subscribers compete for bandwidth over a common coaxial cable, any undesirable reduction in actual data rate is easily controlled simply by limiting the number of shared users on each system. In this manner, each user is assured of a sufficient data rate to provide uninterrupted video teleconferencing or pay-per-view television, for example. BRIEF SUMMARY OF THE INVENTION In a bidirectional communication system, subscriber stations are connected by uplink channels to a receiver at a base station. The individual uplink channels are impaired by user specific noise associated with the respective subscriber stations such as multi-path reflections and the like. In addition, the uplink channels are also impaired by common noise, such as ingress noise, during uplink transmission. Embodiments of the present invention reduce the common noise and/or the individual noise. According to one exemplary embodiment, a base station includes a media access controller (MAC) that generates for downlink transmission MAP messages that assign time slots in which subscriber stations may transmit signal bursts on an uplink channel. The MAP messages include idle slots that are assigned to no subscriber stations. The base station further includes a transmitter and an adaptive notch filter. The transmitter transmits the MAP messages with the idle slots to subscriber stations. The adaptive notch filter has coefficients that are adjusted to suppress noise on the uplink channel sensed during the idle slots. In another exemplary embodiment, a base station includes a notch filter connected to a demodulator. The notch filter has coefficients that are adjustable to cancel noise applied to the demodulator. The base station further includes a MAC and a decision feedback equalizer. The MAC processes binary data and generates for downlink transmission MAP messages. The decision feedback equalizer is coupled to the demodulator and includes a feedforward filter for establishing pre-equalization coefficients. According to another exemplary embodiment, a base station includes means for transmitting on a downlink channel to a plurality of subscriber stations MAP messages that assign time slots in which subscriber stations may transmit signal bursts on an uplink channel. The MAP messages include idle slots that are assigned to no subscriber stations. The base station further includes means for monitoring conditions on the uplink channel during the idle slots. Means for compensating for the monitored conditions on the uplink channel and means for receiving signal bursts on the uplink channel in response to such compensation are also included. In yet another exemplary embodiment, a base station includes means for compensating for noise on an uplink channel and means for receiving on the compensated uplink channel a ranging signal from a subscriber station of a plurality of subscriber stations. The base station further includes means for adjusting filter coefficients to compensate for intersymbol interference on the uplink channel based on the received ranging signal and means for transmitting the adjusted coefficients on a downlink channel to the subscriber station for the purpose of pre-equalization of the uplink channel. In still another exemplary embodiment, a subscriber station includes a transmitter, a receiver, and a transmit equalizer. The transmitter transmits a ranging signal to a base station. The receiver receives pre-equalization coefficients from the base station. The pre-equalization coefficients are based on the ranging signal. The transmit equalizer compensates for noise associated with the subscriber station based on the pre-equalization coefficients. BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES These and other features, aspects and advantages of the present invention will be more fully understood when considered with respect to the following detailed description, appended claims and accompanying drawings wherein: FIG. 1 is a schematic diagram of a hybrid fiber coaxial (HFC) network showing typical pathways for data transmission between the headend (which contains the cable modem termination system) and a plurality of homes (each of which contain a cable modem); FIG. 2 is a simplified block diagram of a cable modem system wherein a line card which defines a cable modem termination system CMTS) is disposed at the headend and a cable modem is disposed within a representative home; FIG. 3 is a simplified block diagram showing the use of a fractional symbol timing loop, a carrier phase correction loop and a conventional amplitude estimator to enhance the rate at which acquisition of data packets is performed in a burst receiver of a cable modem termination system or the like; FIG. 4 is a block diagram showing the interrelationships of the burst transmitter, subscriber medium access control (MAC) and receiver of the cable modem with the burst receiver, medium access control (MAC) and transmitter of the cable modem termination system; FIG. 5A is a schematic block diagram showing the interconnections of the burst receiver, medium access control (MAC) and transmitter downstream modulator within a cable modem termination system; FIG. 5B is a schematic block diagram showing the construction of the cable modem, shown in FIG. 2, at the subscriber, such as the home; FIG. 6A is a block diagram showing a cable modem termination system and a representative cable modem communicating with one another via a cable plant; FIG. 6B is a block diagram showing the cable modem termination system and cable modem of FIG. 2 in further detail; FIG. 6C is a block diagram showing the cable modem termination system of FIG. 2 in further detail; FIG. 6D is a block diagram showing the cable modem of FIG. 3 in further detail; FIG. 6E is a table showing an example of loop filter coarse coefficients and fine coefficients which provide specified bandwidths at the listed update rates; FIGS. 7A and 7B are block diagrams of a sub-system at the subscriber modem for receiving packets with encrypted data and control information, parsing the encrypted data from the control information, decrypting the encrypted data and separately storing the decrypted data and the control information and for restoring the packets with the encrypted data and the control information at the subscriber modem for transmission to the headend; FIGS. 8A and 8B are block diagrams of a sub-system similar to that shown in FIGS. 7A and 7B (but at the headend) for providing a parsing of the signal packets received from the subscriber modem and a decryption of the encrypted data parsed from the packets and for providing an encryption of data for transmission to the subscriber modem and a reformulation of the packets from the encrypted data and the control information; FIG. 9 is a block diagram in some additional detail of a burst receiver shown as a single block in FIG. 4; FIG. 10 is a block diagram in significantly increased detail of the burst receiver shown as a single block in FIG. 4; FIG. 11 is a schematic diagram illustrating the round trip transmission delay between a headend and a subscriber modem; FIG. 12 is a flowchart showing the software level synchronization control of a cable modem; FIG. 13 is a flowchart showing the hardware level synchronization control of a cable modem; FIG. 14 shows a continuous data stream, such as that which may be received by a conventional continuous receiver; FIG. 15 shows a plurality of data bursts separated by guard bands, such as those transmitted by cable modems to a cable modem termination system according to time division multiple access (TDMA); FIG. 16 shows in further detail an exemplary data burst of FIG. 15; FIG. 17 shows the QPSK preamble of FIG. 16 in further detail; FIG. 18 is a block diagram of a contemporary phase locked loop; FIG. 19 is a block diagram of a fractional symbol timing loop in a typical digital receiver, wherein the matched filter is within the loop; FIG. 20 is a block diagram of the fractional symbol timing loop of the present invention, wherein the matched filter has been moved outside the fractional symbol timing loop; FIG. 21 is a block diagram showing a burst receiver having a fractional symbol timing loop, a carrier phase correction loop and an amplitude estimator so as to effect fast acquisition of data packets; FIG. 22 is a block diagram showing a burst receiver having a fractional symbol timing loop, a carrier phase correction loop and an amplitude estimator, wherein the matched filter has been moved outside of the fractional symbol timing loop; FIG. 23 is a block diagram of a phase detector gain boosting logic circuit wherein the amplitude of a signal input to a phase detector is monitored by a sensor and the amplitude of the signal to the low pass filter of the loop is controlled by the output of the sensor; FIG. 24 is a timing diagram showing the use of a single contemporary clock signal to provide timing for a sampling circuit contemporary clock signal (FIG. 24-A) to provide timing for a sampling circuit and also showing the use of two out-of-phase clock signals (FIG. 24-B), wherein and also showing the use of two out-of-phase clock signals, wherein one of the two out-of-phase clock signals will always have a timing relationship relative to the input binary signal to effect sampling of the input binary signal; FIG. 25A is a schematic block diagram of a system for allocating different portions of a dynamic range of power between analog and digital states in the system; FIG. 25B is a schematic block diagram of an RMS estimator that is used to derive a variable gain amplifier setting; FIG. 26 is a block diagram of a prior art technique showing a plurality of contemporary demodulators coupled to demodulate data which is input from a transmission medium such as a fiber optic or coaxial cable and which is coupled to provide the demodulated data as an output thereof; FIG. 27 is a block diagram of one aspect of the present invention, showing a monitoring circuit coupled to monitor a plurality of upstream channels for at least one parameter which is indicative of channel quality; FIG. 28 is a block diagram of a prior art upstream burst receiver and medium access control (MAC) showing modulated data input from a transmission medium, such as a coaxial cable, to the upstream burst receiver and showing digital data output from the MAC; FIG. 29 is a block diagram showing an aspect of the present invention; FIG. 30 is a chart showing RS coding gain for various T's using 16-QAM with K equals 64 bytes; FIG. 31 is a schematic drawing providing an example of fine frequency agility, wherein the frequency spectrum is divided into a plurality of closely spaced channels; FIG. 32 is a flowchart showing dynamic channel allocation control flow; FIG. 33 is a flowchart showing CMTS dynamic channel allocation control flow; FIG. 34 is a simplified block diagram showing the MAC/PHY interface of the present invention; FIG. 35 is a schematic representation of a data packet showing the positioning of the data or payload therein and also showing the location of a guard band; FIG. 36 is a schematic diagram showing the formation of an exemplary MAP which is transmitted by the cable modem termination system (CMTS) to all of the cable modems on a particular channel so as to facilitate communication of the cable modems with the cable modem termination system according to a time division multiple access (TDMA) protocol which avoids collisions among data packets from different cable modems; FIG. 37 is a schematic diagram showing the formation of frames by a cable modem in response to receipt of a MAP, such as that shown in FIG. 36; FIG. 38 is a flowchart showing the operation of the cable modem termination system in separating high priority requests and low priority requests received from cable modems; FIGS. 39 and 40, taken together, define a flowchart showing the operation of the cable modem termination sy