System and method for RF signal combining and adaptive bit loading for data rate maximization in multi-antenna communication systems

• US 7,983,355 B2
• Filed: 07/07/2004
• Issued: 07/19/2011
• Est. Priority Date: 07/09/2003
• Status: Expired due to Fees

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Winters, Jack, Roux, Pieter, Erceg, Vinko, Catreux, Severine, Rooyen, Pieter Van
• Primary Examiner(s): Payne; David C
• Assistant Examiner(s): Wong; Linda
• Application Number:
  US10/886,510
• Publication Number:
  US 20050053164A1
• Time in Patent Office: 2,568 Days
• Field of Search: 375/295, 375/296, 375/316, 455/39, 455/42, 455/45, 455/500, 455/517, 455/522, 455/60, 455/702, 455/703, 455/71
• US Class Current: 375/295
• CPC Class Codes: H04B 7/0615 of weighted versions of same signal
• CPC Class Codes: H04B 7/0842 Weighted combining
• CPC Class Codes: H04L 1/0002 by adapting the transmission rate
• CPC Class Codes: H04L 5/0044 allocation of payload

Abstract

A system and method for generating weight values based on maximum data rate for weighting elements included within signal weighting and combining arrangements used in various multi-antenna transmitter and receiver structures is disclosed herein. Weighting values for a given signal combining arrangement are set so as to maximize an output data rate of the applicable multi-antenna system in the presence of adaptive bit loading of the subcarriers of a transmitted signal. The disclosed techniques may be employed to maximize a data rate of a multi-antenna communication system by using adaptive bit loading and RF and baseband weighting schemes. In this case a search is conducted over various combinations of RF and baseband weights in order to find the weight combination which, when adaptive bit loading is also employed, maximizes the data rate.

Claims

1. In a multi-antenna transmitter disposed to transmit an RF input signal through a plurality of transmit antennas so as to produce a corresponding plurality of RF output signals, said RF input signal being comprised of a plurality of subcarrier signals, an RF signal processing method comprising:

adaptively bit loading said plurality of subcarrier signals in accordance with a corresponding plurality of bit loading values in order to form a corresponding plurality of bit-loaded subcarrier signals, wherein said plurality of bit loaded subcarrier signals are transported by a first transmit path and a second transmit path in the multi-antenna transmitter, wherein said adaptively bit loading comprises individually selecting a respective power scaling factor for each of said plurality of subcarrier signals so that said subcarrier signals characterized by higher signal-to-noise ratios at a remote receiver are allocated more power than said subcarrier signals characterized by lower signal-to-noise ratios at said remote receiver, and wherein said adaptively bit loading comprises individually selecting a respective modulation for each of said plurality of subcarrier signals in which a same modulation is not applied to each of said plurality of subcarrier signals;

converting said plurality of bit-loaded subcarrier signals into said RF input signal in each of said first transmit path and said second transmit path;

dividing said RF input signal, in each of said first transmit path and said second transmit path, in order to form a plurality of at least three divided RF signals;

weighting a first of the divided RF signals from said first transmit path with a first transmit RF weighting value, weighting a first of the divided RF signals from said second transmit path with a second transmit RF weighting weight, and combining said weighted first RF signal from said first transmit path and said weighted first RF signal from said second transmit path before transmitting over a first antenna;

weighting a second of the divided RF signals from said first transmit path with a third transmit RF weighting value, weighting a first of the divided RF signals from said second transmit path with a fourth transmit RF weighting weight, and combining said weighted second RF signal from said first transmit path and said weighted second RF signal from said second transmit path before transmitting over a second antenna; and

weighting a third of the divided RF signals from said first transmit path with a fifth transmit RF weighting value, weighting a first of the divided RF signals from said second transmit path with a sixth transmit RF weighting weight, and combining said weighted third RF signal from said first transmit path and said weighted third RF signal from said second transmit path before transmitting over a third antenna, wherein parameters used for bit loading and transmit RF weighting values are modified as frequently as a particular communication channel changes state.

2. The method of claim 1 wherein said RF input signal comprises an orthogonal frequency division multiplexed signal.

3. The method of claim 1 wherein said plurality of transmit RF weighting values are selected from a plurality of sets of weighting values defining a weight space, the method further including performing a calculation of said output data rate of said transmitter with respect to each of said plurality of sets of weighting values.

4. The method of claim 3 wherein said plurality of subcarrier signals are adaptively bit loaded in connection with each said calculation.

5. The method of claim 1 wherein said plurality of RF output signals are transmitted through a channel and received by a receiver having a set of receive antennas disposed to produce a corresponding set of received RF signals, each of said received RF signals being weighted and combined with at least one other of said received RF signals utilizing a set of receive RF weighting values.

6. The method of claim 5 wherein said plurality of transmit RF weighting values and said set of receive RF weighting values are selected from a plurality of sets of weighting values defining a weight space, the method further including performing a calculation of said output data rate of said transmitter with respect to each of said plurality of sets of weighting values.

7. The method of claim 1 wherein at least said RF transmit weighting values of said transmitter, said RF receive weighting values of said remote receiver and said power scaling factors are jointly determined for said plurality of subcarriers such that an overall data rate over all of said plurality of subcarriers is maximized.

8. The method of claim 1 wherein said plurality of RF weighting values and said plurality of bit loading values are found via a simulated annealing search.

29. The method of claim 5 wherein said plurality of RF weighting values and said plurality of bit loading values are adjusted in accordance with changes in a state of said channel.

9. In a receiver having a plurality of receive antennas disposed to produce a corresponding plurality of received RF signals, each of said plurality of received RF signals being generated in response to a transmitted RF signal comprised of a plurality of subcarrier signals, a signal weighting and combining method comprising:

receiving said plurality of received RF signals by at least three antennas;

dividing said plurality of received RF signals received by each antenna into a first receive path and a second receive path of said receiver;

weighting a first of said divided RF signals of a first antenna with a first RF receive weight, weighting a first of said divided RF signals of a second antenna with a second RF receive weight, weighting a first of said divided RF signals of a third antenna with a third RF receive weight, and combining said first weighted RF signal of said first antenna, said first weighted RF signal of said second antenna and said first weighted RF signal of said third antenna before sending along said first receive path of said receiver;

weighting a second of said divided RF signals of said first antenna with a fourth RF receive weight, weighting a second of said divided RF signals of said second antenna with a fifth RF receive weight, weighting a second of said divided RF signals of said third antenna with a sixth RF receive weight, and combining said second weighted RF signal of the first antenna, said second weighted RF signal of said second antenna and said second weighted RF signal of said third antenna before sending along said second receive path of said receiver, wherein said RF weighting values of said receiver, RF transmit weighting values of a remote transmitter in communication with said receiver, transmit power scaling factors of said remote transmitter, and coded bit rates of said remote transmitter are jointly determined for each of said plurality of subcarrier signals to maximize an overall data rate of all of said plurality of subcarrier signals, wherein the RF weighting values of said receiver and the RF transmit weighting values of the remote transmitter are modified as frequently as a particular communication channel changes state;

downconverting, in each of said first receive path and said second receive path, said one or more combined RF signals into baseband signals;

processing, in parallel, said one or more baseband signals into one or more particular signals, each of said particular signals corresponding to a respective tone of said plurality of subcarrier signals; and

baseband weighting, in parallel, each of said one or more particular signals.

10. The method of claim 9 wherein said transmitted RF signal comprises an orthogonal frequency division multiplexed signal.

11. The method of claim 9 wherein said plurality of RF weighting values are selected from a plurality of sets of weighting values defining a weight space, the method further including performing a calculation of said output data rate with respect to each of said plurality of sets of weighting values.

12. The method of claim 11 wherein said plurality of subcarrier signals are adaptively bit-loaded in connection with each said calculation.

13. The method of claim 9 or 12 wherein said bit-loaded corresponds to one or more of adjusted power, modulation and coding rate.

14. In a communication system including a multi-antenna transmitter disposed to transmit multiple RF input signals through a plurality of transmit antennas so as to produce a corresponding plurality of spatially multiplexed RF output signals, said multiple RF input signals being comprised of corresponding multiple pluralities of subcarrier signals, an RF signal processing method comprising:

adaptively bit loading said multiple pluralities of subcarrier signals in accordance with corresponding multiple pluralities of bit loading values in order to form corresponding multiple pluralities of bit-loaded subcarrier signals, wherein said plurality of bit loaded subcarrier signals are transported by a first transmit path and a second transmit path in the multi-antenna transmitter, wherein said adaptively bit loading comprises individually selecting a respective power scaling factor for each of said plurality of subcarrier signals so that said subcarrier signals characterized by higher signal-to-noise ratios at a remote receiver are allocated more power than said subcarrier signals characterized by lower signal-to-noise ratios at said remote receiver and wherein said adaptively bit loading comprises individually selecting a respective coded bit rate for each of a plurality of subcarrier signals in which a same coded bit rate is not applied to each of said plurality of subcarrier signals;

converting said multiple pluralities of bit-loaded subcarrier signals into said multiple RF input signals in each of said first transmit path and said second transmit path;

dividing said multiple RF input signals, in each of said first transmit path and said second transmit path, in order to form multiple pluralities of at least three divided RF signals;

weighting a first of the divided RF signals from said first transmit path with a first transmit RF weighting value, weighting a first of the divided RF signals from said second transmit path with a second transmit RF weighting weight, and combining said weighted first RF signal from said first transmit path and said weighted first RF signal from said second transmit path before transmitting over a first antenna;

weighting a second of the divided RF signals from said first transmit path with a third transmit RF weighting value, weighting a first of the divided RF signals from said second transmit path with a fourth transmit RF weighting weight, and combining said weighted second RF signal from said first transmit path and said weighted second RF signal from said second transmit path before transmitting over a second antenna; and

weighting a third of the divided RF signals from said first transmit path with a fifth transmit RF weighting value, weighting a first of the divided RF signals from said second transmit path with a sixth transmit RF weighting weight, and combining said weighted third RF signal from said first transmit path and said weighted third RF signal from said second transmit path before transmitting over a third antenna, wherein parameters used for bit loading and transmit RF weighting values are modified as frequently as a particular channel changes state.

15. The method of claim 14 wherein the multiple RF input signals comprise orthogonal frequency division multiplexed signals.

16. The method of claim 14 wherein at least said RF transmit weighting values of said transmitter, said RF receive weighting values of said remote receiver and said power scaling factors are jointly determined for said plurality of subcarriers such that an overall data rate over all of said plurality of subcarriers is maximized.

17. The method of claim 14 wherein said plurality of spatially multiplexed RF output signals are transmitted through a channel and received by a receiver having a set of receive antennas disposed to produce a corresponding set of spatially multiplexed received RF signals, each of said received RF signals further being weighted by a plurality of receive RF weighting values and provided to an RF combining network within said receiver.

18. The method of claim 17 wherein said set of transmit RF weighting values and said plurality of receive RF weighting values are selected from a plurality of sets of weighting values defining a weight space, the method further including calculating said output data rate of said transmitter with respect to each of said plurality of sets of weighting values using multi-user adaptive bit loading.

19. The method of claim 17 wherein said set of transmit RF weighting values, said plurality of receive RF weighting values and said multiple pluralities of bit loading values are found via a simulated annealing search.

20. The method of claim 17 further including:

downconverting a set of RF signals produced by said RF combining network in order to produce a set of baseband signals;

generating pluralities of baseband subcarrier signals using said set of baseband signals; and

weighting and combining ones of said baseband subcarrier signals utilizing a first set of baseband weighting values.

21. The method of claim 20 wherein said set of transmit RF weighting values, said plurality of receive RF weighting values and said first set of baseband weighting values are computed jointly.

22. The method of claim 14 further including performing a splitting and weighting operation upon plural baseband input signals utilizing a second set of baseband weighting values in order to form a second set of baseband signals wherein said multiple pluralities of subcarrier signals are generated based upon one or more of said second set of baseband signals.

23. The method of claim 22 wherein said set of transmit RF weighting values, said plurality of receive RF weighting values and said first and second set of baseband weighting values are computed jointly.

24. In a receiver having a plurality of receive antennas disposed to produce a corresponding plurality of spatially multiplexed received RF signals in response to spatially multiplexed transmitted RF signal energy, said transmitted RF signal energy being comprised of multiple pluralities of subcarrier signals, a signal weighting and combining method comprising:

receiving said plurality of received RF signals by at least three antennas;

dividing said plurality of received RF signals received by each antenna into a first receive path and a second receive path of said receiver;

weighting a first of said divided RF signals of a first antenna with a first RF receive weight, weighting a first of said divided RF signals of a second antenna with a second RF receive weight, weighting a first of said divided RF signals of a third antenna with a third RF receive weight, and combining said first weighted RF signal of said first antenna, said first weighted RF signal of said second antenna and said first weighted RF signal of said third antenna before sending along said first receive path of said receiver;

weighting a second of said divided RF signals of said first antenna with a fourth RF receive weight, weighting a second of said divided RF signals of said second antenna with a fifth RF receive weight, weighting a second of said divided RF signals of said third antenna with a sixth RF receive weight, and combining said second weighted RF signal of the first antenna, said second weighted RF signal of said second antenna and said second weighted RF signal of said third antenna before sending along said second receive path of said receiver, wherein said RF weighting values of said receiver, RF transmit weighting values of a remote transmitter in communication with said receiver, transmit power scaling factors of said remote transmitter, and coded bit rates of said remote transmitter are jointly determined for each of said plurality of subcarrier signals to maximize an overall data rate of all of said plurality of subcarrier signals, wherein the RF weighting values of said receiver and the RF transmit weighting values of said remote transmitter are modified as frequently as a particular channel changes state.

25. The method of claim 24 wherein each of said multiple pluralities of subcarrier signals comprises an orthogonal frequency division multiplexed signal.

26. The method of claim 24 wherein said spatially multiplexed transmitted RF signal energy is composed of multiple pluralities of RF signals, each of said multiple pluralities of RF signals being weighted by a corresponding plurality of transmit RF weighting values.

27. The method of claim 26 wherein said plurality of transmit and receive RF weighting values are selected from a plurality of sets of weighting values defining a weight space, the method further including calculating said output data rate with respect to each of said plurality of sets of weighting values using multi-user adaptive bit loading.

28. The method of claim 24 further including:

downconverting said one or more spatially-multiplexed combined RF signals in order to produce a set of baseband signals;

generating pluralities of baseband subcarrier signals using said set of baseband signals; and

weighting and combining ones of said baseband subcarrier signals utilizing a first set of baseband weighting values.