Backward-compatible long training sequences for wireless communication networks

Abstract

A network device for generating an expanded long training sequence with a minimal peak-to-average ratio. The network device includes a signal generating circuit for generating the expanded long training sequence. The network device also includes an Inverse Fourier Transform for processing the expanded long training sequence from the signal generating circuit and producing an optimal expanded long training sequence with a minimal peak-to-average ratio. The expanded long training sequence and the optimal expanded long training sequence are stored on more than 52 sub-carriers.

Claims

.[.1. A wireless communications device, comprising: a signal generator that generates an extended long training sequence; and an Inverse Fourier Transformer operatively coupled to the signal generator, wherein the Inverse Fourier Transformer processes the extended long training sequence from the signal generator and provides an optimal extended long training sequence with a minimal peak-to-average ratio, and wherein at least the optimal extended long training sequence is carried by a greater number of subcarriers than a standard wireless networking configuration for an Orthogonal Frequency Division Multiplexing scheme..].

.[.2. The wireless communications device according to claim 1, wherein at least the optimal extended long training sequence is carried by at least 56 active sub-carriers..].

.[.3. The wireless communications device according to claim 2, wherein the at least 56 active sub-carriers correspond to at least indexed sub-carriers −28 to +28..].

.[.4. The wireless communications device according to claim 2, wherein the optimal extended long training sequence has a minimum peak-to-average power ratio of 3.6 dB..].

.[.5. The wireless communications device according to claim 1, wherein at least the optimal extended long training sequence is carried by at least 63 active sub-carriers..].

.[.6. The wireless communications device according to claim 5, wherein the at least 63 active sub-carriers correspond to at least indexed sub-carriers −32 to +31..].

.[.7. The wireless communications device according to claim 5, wherein the optimal extended long training sequence has a minimum peak-to-average power ratio of 3.6 dB..].

.[.8. The wireless communications device according to claim 1, wherein a binary phase shift key encoding is used for each sub-carrier above the +26 indexed sub-carrier and below the −26 indexed sub-carrier..].

.[.9. The wireless communications device according to claim 1, wherein the Inverse Fourier Transformer comprises at least one of the following: an Inverse Fast Fourier Transformer and an Inverse Discrete Fourier Transformer..].

.[.10. The wireless communications device according to claim 1, wherein the wireless communications device comprises one or more of the following: a personal digital assistant, a laptop computer, a personal computer and a cellular phone..].

.[.11. The wireless communications device according to claim 1, wherein the wireless communications device comprises a wireless mobile communications device..].

.[.12. The wireless communications device according to claim 1, wherein the wireless communications device comprises one or more of the following: an access point and a base station..].

.[.13. The wireless communications device according to claim 1, wherein the wireless communications device is backwards compatible with legacy wireless local area network devices..].

.[.14. The wireless communications device according to claim 1, wherein the optimal extended long training sequence is longer than a long training sequence used by a legacy wireless local area network device in accordance with a legacy wireless networking protocol standard..].

.[.15. The wireless communications device according to claim 14, wherein the legacy wireless local area network device uses the optimal extended long training sequence to estimate a carrier frequency offset even though the optimal extended long training sequence is longer than the long training sequence that is specified by the legacy wireless networking protocol standard..].

.[.16. The wireless communications device according to claim 15, wherein the long training sequence that is specified by the legacy wireless networking protocol standard is maintained in the extended long training sequence or the optimal extended long training sequence..].

.[.17. The wireless communications device according to claim 1, wherein the wireless communications device decreases power back-off..].

.[.18. The wireless communications device according to claim 1, wherein the wireless communications device registers with one or more of the following: an access point and a base station..].

.[.19. The wireless communications device according to claim 1, wherein the extended long training sequence or the optimal extended long training sequence is encoded using binary phase shift key encoding on each of the subcarriers..].

.[.20. The wireless communications device according to claim 1, comprising: a symbol mapper operatively coupled to the signal generator, wherein the symbol mapper receives coded bits and generates symbols for each of 64 subcarriers of an Orthogonal Frequency Division Multiplexing sequence..].

.Iadd.21. A wireless communications device, comprising: a signal generator that generates an extended long training sequence; and an Inverse Fourier Transformer operatively coupled to the signal generator, wherein the Inverse Fourier Transformer processes the extended long training sequence from the signal generator and provides an optimal extended long training sequence with a minimal peak-to-average ratio, and wherein at least the optimal extended long training sequence is carried by a greater number of subcarriers than a standard wireless networking configuration for an Orthogonal Frequency Division Multiplexing scheme, and wherein the optimal extended long training sequence is carried by exactly 56 active sub-carriers..Iaddend.

.Iadd.22. The wireless communications device according to claim 21, wherein the optimal extended long training sequence has a minimum peak-to-average power ratio of 3.6 dB..Iaddend.

.Iadd.23. The wireless communications device according to claim 21, wherein a binary phase shift key encoding is used for each sub-carrier above the +26 indexed sub-carrier and below the −26 indexed sub-carrier..Iaddend.

.Iadd.24. The wireless communications device according to claim 21, wherein the Inverse Fourier Transformer comprises an Inverse Fast Fourier Transformer or an Inverse Discrete Fourier Transformer..Iaddend.

.Iadd.25. The wireless communications device according to claim 21, wherein the wireless communications device comprises one or more of the following: a personal digital assistant, a laptop computer, a personal computer, a processor, and a cellular phone..Iaddend.

.Iadd.26. The wireless communications device according to claim 21, wherein the wireless communications device comprises a wireless mobile communications device..Iaddend.

.Iadd.27. The wireless communications device according to claim 21, wherein the wireless communications device comprises one or more of the following: an access point and a base station..Iaddend.

.Iadd.28. The wireless communications device according to claim 21, wherein the wireless communications device is backwards compatible with legacy wireless local area network devices..Iaddend.

.Iadd.29. The wireless communications device according to claim 21, wherein the optimal extended long training sequence is longer than a long training sequence used by a legacy wireless local area network device in accordance with a legacy wireless networking protocol standard..Iaddend.

.Iadd.30. The wireless communications device according to claim 29, wherein the legacy wireless local area network device uses the optimal extended long training sequence to estimate a carrier frequency offset even though the optimal extended long training sequence is longer than the long training sequence that is specified by the legacy wireless networking protocol standard..Iaddend.

.Iadd.31. The wireless communications device according to claim 30, wherein the long training sequence that is specified by the legacy wireless networking protocol standard is maintained in the extended long training sequence or the optimal extended long training sequence..Iaddend.

.Iadd.32. The wireless communications device according to claim 29, wherein the legacy wireless networking protocol standard for the Orthogonal Frequency Division Multiplexing scheme corresponds to exactly 52 active subcarriers..Iaddend.

.Iadd.33. The wireless communications device according to claim 32, wherein, for a long training sequence of the legacy wireless networking protocol standard, the indexed sub-carrier 0 is set to zero and encodings for the indexed sub-carriers −26 to +26 excluding the indexed sub-carrier 0 are: TABLE-US-00001 Sub- −26 −25 −24 −23 −22 −21 −20 −19 −18 −17 −16 −15 −14  carrier Encoding +1 +1 −1 −1 +1 +1 −1 +1 −1 +1 +1 +1 +1  Sub- −13 −12 −11 −10 −9 −8 −7 −6 −5 −4 −3 −2 4  carrier Encoding +1 +1 −1 −1 +1 +1 −1 +1 −1 +1 +1 +1 +1  Sub- 1 2 3 4 5 6 7 8 9 10 11 12 13  carrier Encoding +1 −1 4 +1 +1 4 +1 4 +1 4 4 4 4  Sub- 14 15 16 17 18 19 20 21 22 23 24 25 26  carrier Encoding −1 +1 +1 −1 −1 +1 −1 +1 −1 +1 +1 +1 +1. .Iaddend.

.Iadd.34. The wireless communications device according to claim 33, wherein: the Inverse Fourier Transformer comprises an Inverse Fast Fourier Transformer or an Inverse Discrete Fourier Transformer; the wireless communications device comprises one or more of the following: a personal digital assistant, a laptop computer, a personal computer, a cellular phone, an access point, a processor, and a base station; the wireless communications device is backwards compatible with the legacy wireless local area network device; the legacy wireless local area network device uses the optimal extended long training sequence to estimate a carrier frequency offset even though the optimal extended long training sequence is longer than the long training sequence that is specified by the legacy wireless networking protocol standard; the wireless communications device decreases power back-off; the extended long training sequence or the optimal extended long training sequence is encoded using binary phase shift key encoding on each of the 56 active subcarriers; and the wireless communications device further comprises a symbol mapper operatively coupled to the signal generator, wherein the symbol mapper receives coded bits and generates symbols for each of 64 subcarriers of an Orthogonal Frequency Division Multiplexing sequence..Iaddend.

.Iadd.35. The wireless communications device according to claim 21, wherein the wireless communications device decreases power back-off..Iaddend.

.Iadd.36. The wireless communications device according to claim 21, wherein the wireless communications device registers with one or more of the following: an access point and a base station..Iaddend.

.Iadd.37. The wireless communications device according to claim 21, wherein the extended long training sequence or the optimal extended long training sequence is encoded using binary phase shift key encoding on each of the 56 active subcarriers..Iaddend.

.Iadd.38. The wireless communications device according to claim 21, comprising: a symbol mapper operatively coupled to the signal generator, wherein the symbol mapper receives coded bits and generates symbols for each of 64 subcarriers of an Orthogonal Frequency Division Multiplexing sequence..Iaddend.

.Iadd.39. The wireless communications device according to claim 21, wherein at least one output of the Inverse Fourier Transformer is operatively coupled to at least one digital-to-analog converter..Iaddend.

.Iadd.40. The wireless communications device according to claim 21, wherein at least one output of the Inverse Fourier Transformer is operatively coupled to multiple digital-to-analog converters..Iaddend.

.Iadd.41. The wireless communications device according to claim 21, wherein an input of the signal generator is operatively coupled to a frequency-domain windower..Iaddend.

.Iadd.42. The wireless communications device according to claim 21, wherein an output of the Inverse Fourier Transformer is operatively coupled to a time-domain windower..Iaddend.

.Iadd.43. The wireless communications device according to claim 42, wherein an output of the time-domain windower is operatively coupled to at least one digital-to-analog converter..Iaddend.

.Iadd.44. The wireless communication device according to claim 21, wherein an output of the Inverse Fourier Transformer is operatively coupled to a digital transmit filter..Iaddend.

.Iadd.45. The wireless communications device according to claim 21, wherein an output of the Inverse Fourier Transformer is operatively coupled to a parallel-to-serial convertor..Iaddend.

.Iadd.46. The wireless communications device according to claim 21, wherein the optimal extended long training sequence is represented by encodings for indexed sub-carriers −28 to +28, excluding indexed sub-carrier 0 which is set to zero..Iaddend.

.Iadd.47. The wireless communications device according to claim 21, wherein the wireless communications device is configured to convert parallel frequency-domain signals into serial time-domain signals..Iaddend.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention that together with the description serve to explain the principles of the invention, wherein:

(2) FIG. 1 illustrates a communication system that includes a plurality of base stations, a plurality of wireless communication devices and a network hardware component;

(3) FIG. 2 illustrates a schematic block diagram of a processor that is configured to generate an expanded long training sequence;

(4) FIG. 3 is a schematic block diagram of a processor that is configured to process an expanded long training sequence;

(5) FIG. 4 illustrates the long training sequence that is used in 56 active sub-carriers; and

(6) FIG. 5 illustrates the long training sequence that is used in 63 active sub-carriers.

DETAILED DESCRIPTION OF THE INVENTION

(7) Reference will now be made to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

(8) FIG. 1 illustrates a communication system 10 that includes a plurality of base stations and/or access points 12-16, a plurality of wireless communication devices 18-32 and a network hardware component 34. Wireless communication devices 18-32 may be laptop computers 18 and 26, personal digital assistant hosts 20 and 30, personal computer 24 and 32 and/or cellular telephone 22 and 28. Base stations or access points 12-16 are operably coupled to network hardware 34 via local area network connections 36, 38 and 40. Network hardware 34, for example a router, a switch, a bridge, a modem, or a system controller, provides a wide area network connection for communication system 10. Each of base stations or access points 12-16 has an associated antenna or antenna array to communicate with the wireless communication devices in its area. Typically, the wireless communication devices register with a particular base station or access point 12-14 to receive services from communication system 10. Each wireless communication device includes a built-in radio or is coupled to an associated radio. The radio includes at least one radio frequency (RF) transmitter and at least one RF receiver.

(9) The present invention provides an expanded long training sequence of minimum peak-to-average power ratio and thereby decreases power back-off. The inventive expanded long training sequence may be used by 802.11a or 802.11g devices for estimating the channel impulse response and by a receiver for estimating the carrier frequency offset between the transmitter clock and receiver clock. The inventive expanded long training sequence is usable by 802.11a or 802.11g systems only if the values at sub-carriers −26 to +26 are identical to those of the current long training sequence used in 802.11a and 802.11g systems. As such, the invention .[.utilized.]. .Iadd.utilizes .Iaddend.the same +1 or −1 binary phase shift key (BPSK) encoding for each new sub-carrier and the long training sequence of 802.11a or 802.11g systems is maintained in the present invention.

(10) In a first embodiment of the invention, the expanded long training sequence is implemented in 56 active sub-carriers including sub-carriers −28 to +28 .Iadd.except the 0-index sub-carrier which is set to 0.Iaddend.. In another embodiment, an expanded long training sequence is implemented using 63 active sub-carriers, i.e., all of the active sub-carriers (−32 to +31) except the 0-index sub-carrier which is set to 0. In both embodiments of the invention, orthogonality is not affected, since a 64-point orthogonal transform is used to generate the time-domain sequence. Additionally, the output of an auto-correlator for computing the carrier frequency offset is not affected by the extra sub-carriers.

(11) FIG. 2 illustrates a schematic block diagram of a processor that is configured to generate an expanded long training sequence. Processor 200 includes a symbol mapper 202, a frequency domain window 204, a signal generating circuit 205, an inverse .[.fast.]. Fourier transform .[.(IFFT).]. module 206, a .[.serial to.]. parallel .Iadd.to serial .Iaddend.module 208, a digital transmit filter and/or time domain window module 210, and digital to analog converters (D/A) 212. For an expanded long training sequence, symbol mapper 202 generates symbols from the coded bits for each of the 64 subcarriers of an OFDM sequence. Frequency domain window 204 applies a weighting factor on each subcarrier. Signal generating circuit 205 generates the expanded long training sequence and if 56 active sub-carriers are being used, signal generating circuit generates the expanded long training sequence and stores the expanded long training sequence in sub-carriers −28 to +28 .Iadd.except the 0-index sub-carrier which is set to 0.Iaddend.. If 63 active sub-carriers are being used, signal generating circuit generates the expanded long training sequence and stores the expanded long training sequence in sub-carriers −32 to +32 i.e., all of the active sub-carriers (−32 to +31) except the 0-index sub-carrier which is set to 0. The inventive long training sequence is inputted into an Inverse Fourier Transform 206. The invention uses the same +1 or −1 BPSK encoding for each new sub-carrier. Inverse Fourier Transform 206 may be an inverse Fast Fourier Transform (IFFT) or Inverse Discrete Fourier Transform .[.(IFDT).]. .Iadd.(IDFT).Iaddend.. Inverse Fourier Transform 206 processes the long training sequence from signal generating circuit 205 and thereafter produces an optimal expanded long training sequence with a minimal peak-to-average power ratio. The optimal expanded long training sequence may be used in either 56 active sub-carriers or 63 active subscribers. .[.Serial to parallel.]. .Iadd.Parallel to serial .Iaddend.module 208 converts the .[.serial.]. .Iadd.parallel .Iaddend.time domain signals .Iadd.from the Inverse Fourier Transform 206 .Iaddend.into .[.parallel.]. .Iadd.serial .Iaddend.time domain signals that are subsequently filtered and converted to analog signals via the D/A.

(12) FIG. 3 is a schematic block diagram of a processor that is configured to process an expanded long training sequence. Processor 300 includes a symbol demapper 302, a frequency domain window 304, a fast Fourier transform (FFT) module 306, a .[.parallel to.]. serial .Iadd.to parallel .Iaddend.module 308, a digital receiver filter and/or time domain window module 310, and analog to digital converters (A/D) 312. A/D converters 312 convert the sequence into digital signals that are filtered via digital receiver filter 310. .[.Parallel to serial.]. .Iadd.Serial to parallel .Iaddend.module 308 converts the digital time domain signals into a plurality of .[.serial.]. time domain signals. FFT module 306 converts the .[.serial.]. time domain signals into frequency domain signals. Frequency domain window 304 applies a weighting factor on each frequency domain signal. Symbol demapper 302 generates the coded bits from each of the 64 subcarriers of an OFDM sequence received from the frequency domain window.

(13) FIG. 4 illustrates the long training sequence with a minimum peak-to-average power ratio that is used in 56 active sub-carriers. Out of the 16 possibilities for the four new sub-carrier positions, the sequence illustrated in FIG. 4 has the minimum peak-to-average power ratio, i.e., a peak-to-average power ratio of 3.6 dB.

(14) FIG. 5 illustrates the long training sequence with a minimum peak-to-average power ratio that is used in 63 active sub-carriers. Out of the 2048 possibilities for the eleven new sub-carrier positions, the sequence illustrated in FIG. 5 has the minimum peak-to-average power ratio, i.e., a peak-to-average power ratio of 3.6 dB.

(15) It should be appreciated by one skilled in art, that the present invention may be utilized in any device that implements the OFDM encoding scheme. The foregoing description has been directed to specific embodiments of this invention. It will be apparent, however, that other variations and modifications may be made to the described embodiments, with the attainment of some or all of their advantages. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention.