Adaptive modulation for fixed wireless link in cable transmission system

• US 20020075830A1
• Filed: 05/15/2001
• Published: 06/20/2002
• Est. Priority Date: 10/16/2000
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Hartman, David L. Jr.
• Granted Patent: US 7,016,296 B2
• Time in Patent Office: Days
• US Class Current: 370/333
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0025 Transmission of mode-switching indication
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0037 Inter-user or inter-terminal allocation

Abstract

Methods and systems for communicating on a wireless channel are provided which enable subscribers that share the channel to transmit using different modulation schemes. The modulation scheme used by each subscriber is assigned to the subscriber by a wireless access termination system. The modulation scheme assigned to a subscriber by the wireless access termination system is determined based on measurements of the quality of signals received from that subscriber. In one embodiment, the invention includes a transmitter and a receiver. The receiver is capable of transmitting data using one of a number of encoding and symbol constellation configurations. The receiver is also capable of receiving a first signal. Receiving the first signal causes the transmitter to transmit a second signal using a specified encoding and symbol constellation configuration.

Claims

1. A wireless transmission system comprising:

a wireless vector orthogonal frequency division multiple access transmitter for sending data using an encoding scheme and symbol constellation;

a memory accessible to the transmitter for storing a plurality of encoding scheme and symbol constellation transmitter configurations;

a wireless vector orthogonal frequency division multiple access receiver for intercepting data sent by the transmitter;

means for measuring one or more parameters of the intercepted data at the receiver, such parameters being indicative of the quality of transmission;

means responsive to the measured quality falling below a threshold value for sending from the receiver a request to change the encoding scheme and/or symbol constellation being used by the transmitter; and

means for substituting for the encoding scheme and symbol constellation being used by the transmitter another encoding scheme and symbol constellation stored in said memory.

2. The wireless transmission system of claim 1, wherein said measured parameters include at least one of average SINR, SINR variance, DER, CER, SER, channel power, corrected bit errors, corrected codeword errors, Ricean K-factor or the Viterbi decoder path metrics.

3. The wireless transmission system of claim 1, wherein said quality of transmission is determined using the function:

4. The wireless transmission system of claim 1, wherein:

at least one of said plurality of encoding scheme and symbol constellation transmitter configurations comprises Reed-Solomon encoding capable of correcting a first number of byte errors per codeword and a convolutional encoding of a first rate; and

at least one of said plurality of encoding scheme and symbol constellation configurations utilizes one of QPSK, 16-QAM or 64-QAM as its symbol constellation.

5. A wireless modem comprising:

a vector orthogonal frequency division multiple access transmitter for sending data using an encoding scheme and symbol constellation;

a memory accessible to said transmitter for storing a plurality of encoding scheme and symbol constellation configurations;

a receiver for receiving a first signal indicative of one of said encoding scheme and symbol constellation configurations;

means for substituting the encoding scheme and symbol constellation configuration indicated by said first signal for the encoding scheme and symbol constellation configuration being used by the transmitter.

6. A wireless modem comprising:

a transmitter for sending data using an encoding scheme and symbol constellation;

a memory accessible to said transmitter for storing a plurality of encoding scheme and symbol constellation configurations;

a receiver for receiving a first signal indicative of one of said encoding scheme and symbol constellation configurations;

means for encoding data using a concatenated encoding scheme involving Reed-Solomon encoding capable of correcting a specified number of bit errors and convolutional encoding of a specified rate;

means for transmitting signals using a symbol constellation chosen from a set of symbol constellations comprising QPSK, 16-QAM and 64-QAM;

means for configuring said encoding means to encode data using the encoding scheme indicated by said first signal; and

means for configuring said means for transmitting signals to transmit using the symbol constellation indicated by said first signal.

7. The wireless modem of claim 6, wherein said transmitter is a vector orthogonal frequency division multiple access transmitter.

8. A wireless termination system comprising:

a vector orthogonal frequency division multiple access receiver for receiving a first signal;

a transmitter for sending a second signal indicative of an encoding scheme and symbol constellation configuration;

means for measuring the quality of said first signal; and

means for causing transmitter to send said second signal in response to said measured quality of the first signal.

9. The wireless termination system of claim 8, further comprising:

a memory accessible to said transmitter for storing a plurality of encoding scheme and symbol constellation configurations and ranges of qualities for each configuration;

means for determining which of said ranges of qualities contains said measured quality of signal;

means for choosing said encoding scheme and symbol constellation associated with said range of qualities which contains said measured quality of the first signal as the symbol constellation configuration indicated by said second signal.

10. The wireless termination system of claim 9, wherein quality of said signal is measured using at least one of average SINR, SINR variance, BER, CER, SER, channel power, corrected bit errors, corrected codeword errors, Ricean K-factor or the Viterbi decoder path metrics.

11. The wireless termination system of claim 9, wherein quality of said first signal is measured as the sum:

12. The wireless termination system of claim 9, wherein:

at least one of said plurality of encoding scheme and symbol constellation configurations comprises Reed-Solomon encoding capable of correcting a first number of byte errors per codeword and a convolutional encoding of a first rate; and

at least one of said plurality of encoding scheme and symbol constellation configurations utilizes one of QPSK, 16-QAM or 64-QAM as its symbol constellation.

14. The method of claim 13, wherein quality of said first signal is measured using at least one of average SINR, SINR variance, BER, CER, SER, channel power, corrected bit errors, corrected codeword errors, Ricean K-factor or Viterbi path metrics.

15. The method of claim 13, wherein quality of said first signal is measured as the sum:

16. The method of claim 13, further comprising the step of:

said transmitting unit transmitting a fourth signal to said receiving unit;

said transmitting unit using a first encoding method and first modulation method to encode and modulate said first signal;

if said transmitting unit receives said second signal, then said transmitting unit using a second encoding method and second modulation method to encode and modulate said fourth signal;

if said transmitting unit receives said third signal, then said transmitting unit using a third encoding method and third modulation method to encode and modulate said fourth signal; and

if said transmitting unit does not receive either of said second signal or said third signal, then said transmitting unit using said first encoding method and first modulation method to encode and modulate said fourth signal.

17. The method of claim 16, wherein:

said first encoding method comprises a concatenated code involving Reed-Solomon encoding capable of correcting a first number of bit errors and convolutional encoding of a first rate; and

said first modulation method uses one of a set of symbol constellations comprising QPSK, 16-QAM or 64-QAM.

18. The method of claim 17, wherein:

said second encoding method comprises a concatenated code involving Reed-Solomon encoding capable of correcting a second number of bit errors and convolutional encoding of a second rate;

said second modulation method is one of a set of symbol constellations comprising QPSK, 16-QAM or 64-QAM;

said third encoding method comprises a concatenated code involving Reed-Solomon encoding capable of correcting a third number of bit errors and convolutional encoding of a third rate; and

said third modulation method is one of a set of symbol constellations comprising QPSK, 16-QAM or 64-QAM.

20. The method of claim 19, further comprising the steps of:

i. said receiver comparing said chosen encoding scheme and symbol constellation transmission configuration to said first encoding scheme and symbol constellation configuration; and

j. if said chosen encoding scheme and symbol constellation transmission configuration is not the same as said first encoding scheme and symbol constellation configuration, then said receiver transmitting a second signal to said transmitter indicative of chosen encoding scheme and symbol constellation transmission configuration.

21. The method of claim 19, wherein quality of said first signal is measured using at least one of average SINR, SINR variance, BER, CER, SER, channel power, corrected bit errors, corrected codeword errors, Ricean K-factor or Viterbi path metrics.

22. The method of claim 19, wherein quality of first signal is measured as the sum:

23. The method of claim 19, wherein said lower operating thresholds and said upper operating thresholds of said plurality of encoding scheme and symbol constellation transmission configurations are chosen to incorporate hysteresis.

13. A method of transmitting information between a transmitting unit and a receiving unit comprising the steps of:

said transmitting unit transmitting a first signal to said receiving unit using a vector orthogonal frequency division multiple access signal;

said receiving unit measuring quality of said first signal;

if measured quality of said first signal does not satisfy a set of lower thresholds, then said receiving unit transmitting a second signal to said transmitting unit; and

if measured quality of said second signal does not satisfy a set of upper thresholds, then said receiving unit transmitting a third signal to said transmitting unit.

19. A method of choosing an encoding scheme and symbol constellation transmission configuration for the transmission of a data signal between a transmitter and a receiver from a plurality of encoding scheme and symbol constellation transmission configurations, each having a lower operating threshold and an upper operating threshold, comprising the steps of:

a. said transmitter transmitting a first signal using a first encoding scheme and symbol constellation transmission configuration;

b. said receiver measuring the quality of said first signal;

c. the receiver selecting the first encoding scheme and symbol constellation transmission configuration as a selected encoding scheme and symbol constellation transmission configuration;

d. said receiver comparing said measured quality of signal to said lower operating threshold associated with said selected encoding scheme and symbol constellation transmission configuration;

e. if said measured quality of the first signal does not satisfy said lower operating threshold in step b., then said receiver selecting from said plurality of encoding scheme and symbol constellation transmission configurations a second encoding scheme and symbol constellation transmission configuration that has a more robust encoding scheme and/or a smaller symbol constellation as said selected encoding scheme and symbol constellation transmission configuration and repeating step b.;

f. said receiver comparing said selected encoding scheme and symbol constellation configuration to said upper operating threshold;

g. if said measured quality of the first signal does not satisfy said upper operating threshold in step f., then said receiver selecting from said plurality of encoding scheme and symbol constellation transmission configurations a third encoding scheme and symbol constellation transmission configuration that has a less robust encoding scheme and/or a larger symbol constellation as said selected encoding scheme and symbol constellation transmission configuration and repeating step f.;

h. said receiver choosing selected encoding scheme and symbol constellation transmission configuration as said encoding scheme and symbol constellation for transmission of said data signal between said transmitter and said receiver.

24. A method of allocating transmission time slots on a time division multiple access wireless channel to a transmitter, which transmits a plurality of traffic streams using one of a plurality of encoding and modulation schemes and wherein each traffic stream has a specified quality of service comprising the steps of:

a. allocating a number of said transmission time slots to said transmitter to ensure said quality of service requirements for each of said traffic streams transmitted by said transmitter are satisfied;

b. monitoring quality of transmissions from said transmitter;

c. if said transmission quality decreases below a lower threshold, then instructing said transmitter to transmit using a second of said plurality of encoding and modulation schemes that is more robust than the encoding and modulation scheme being used by said transmitter and allocating additional timeslots to said transmitter to ensure said quality of service requirements of said traffic streams are satisfied when said transmitter transmits using said second encoding and modulation scheme; and

d. if said quality of transmission increases above an upper threshold, then instructing said transmitter to transmit using a third of said plurality of encoding and modulation schemes that is less robust than the encoding and modulation scheme being used by said transmitter and reallocating time slots not required by said transmitter to meet said quality of service requirements of said traffic streams when the transmitter transmits using said third encoding and modulation scheme.