Multicarrier personal access communication system

• US 6,449,246 B1
• Filed: 12/30/1999
• Issued: 09/10/2002
• Est. Priority Date: 09/15/1999
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Telcordia Technologies Incorporated (Telefonaktiebolaget LM Ericsson)
• Inventors: Wong, Kuok-Shoong Daniel, Barton, Melbourne
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): Milord, Marceau
• Application Number:
  US09/475,219
• Time in Patent Office: 985 Days
• Field of Search: 370/328, 370/203, 370/206, 370/210, 370/343, 370/344, 375/362, 375/260, 375/261, 375/265, 455/42, 455/46, 455/47
• US Class Current: 370/210
• CPC Class Codes: H04L 2025/03522 Frequency domain
• CPC Class Codes: H04L 27/262 Reduction thereof by selection of pilot symbols
• CPC Class Codes: H04L 27/2627 Modulators
• CPC Class Codes: H04L 27/26524 Fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators in combination with other circuits for demodulation
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/3411 reducing the peak to average power ratio or the mean power of the constellation; Arrangements for increasing the shape gain of a signal set
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601

Abstract

A highly modular PACS-based system that combines the advantages of Optical Frequency Division Multiplexing (OFDM) and Personal Access Communication System (PACS) with Time Division Multiple Access (TDMA) technology. The system is arranged to support high-speed (higher than the 32 kbps of PACS) wireless access services to fixed and mobile users. For example, nominal user data rates of 32-to-356 kbps are attainable, and ever the higher speed of 768 kbps is possible for short ranges.

Claims

1. A method for communicating a sequence of input bits over a wireless channel from a transmitter to a receiver to produce a sequence of output bits from the receiver corresponding to the sequence of input bits, the method comprising the steps of

converting in the transmitter the sequence of input bits into a corresponding set of input symbols wherein each of the input symbols represents a unique plurality of the input bits,

modulating in the transmitter each of the input symbols to produce a corresponding set of complex symbols,

computing in the transmitter the inverse Discrete Fourier Transform of the set of complex symbols to produce a transformed set of symbols,

augmenting in the transmitter the transformed set of symbols with cyclic prefix symbols determined with reference to the transformed set to produce a set of output symbols,

processing in the transmitter the set of output symbols to generate a radio frequency signal at a given carrier frequency, the radio frequency signal including carrier synchronization information and complex symbol timing information to recover the output symbols,

propagating the radio frequency signal over the wireless channel from the transmitter,

recovering in the receiver the carrier frequency synchronization information and recovering the complex symbol timing information from the radio frequency signal,

processing in the receiver the radio frequency signal using the recovered carrier frequency synchronization and the recovered timing information to produce a stream of recovered complex symbols,

removing in the receiver the cyclic prefix symbols from the recovered complex symbols to produce a reduced set of complex symbols,

computing in the receiver the Discrete Fourier transform of the reduced set of complex symbols to produce a set of detected complex symbols, and

demodulating in the receiver the detected complex symbols to generate the sequence of output bits.

2. The method as recited in claim 1 wherein each of the complex symbols has an in-phase component and a quadrature component expressed as a pair for a given modulation technique, and wherein the step of modulating comprises the steps of

accessing a minimal energy constellation of points expressed as pairs of in-phase and quadrature components representative of the given modulation technique wherein the number of points equals the number of combinations of input bits in any of the input symbols and such that each of the points is assigned a unique one of the combinations, and

selecting the in-phase and quadrature components of one of the points for each of the input symbols as the corresponding one of the complex symbols.

3. The method as recited in claim 2 further including the steps of

determining the minimal energy constellation of points upon initialization of the method, and

storing the constellation for accessibility by the step of modulating.

4. The method as recited in claim 3 wherein the given modulation technique is M-level Quadrature Amplitude Modulation (M-QAM) and the step of determining includes the steps of

defining a set of constellation points for the M-QAM constellation as S_M,

labeling, for the 4-QAM constellation, the point in S₄ having x and y coordinates as P₀→

(x,y), and

labeling the other three points in a counter-clockwise direction to complete the 4-QAM constellation as P₁→

(−

x,y), P₂→

(−

x,−

y), and P₃→

(x,−

y).

5. The method as recited in claim 4 wherein the step of determining further includes, after the second step of labeling, the step of assigning codes to the 4-QAM constellation points based on a Gray code assignment.

6. The method as recited in claim 4 wherein the step of determining further includes, after the second step of labeling, the steps of

iteratively labeling constellation points for 8-QAM and higher by defining the next point P_k→

(x,y) in S_M not already in S<sub>M−

1</sub> and determining the lowest energy point x²+y² not in S<sub>M−

1</sub> using the following rules if two or more points have equal energy;

Rule 1—

if the sums (x+y) for the points are equal, choose the point with the smallest y value;

Rule 2—

if the sums are different, choose the point with the smallest max {x,y},

choosing the three points associated with P_k as P_k+1→

(−

x,y), P_k+2→

(−

x,−

y), and P_k+3→

(x,−

y), and

repeating the iteratively labeling and choosing steps until there are M/4 points in S_M.

7. The method as recited in claim 6 wherein the step of determining further includes the step of assigning codes to the constellation points based on a Gray code assignment whenever feasible.

8. The method as recited in claim 1 wherein each of the complex symbols in the reduced set has an in-phase component and a quadrature component expressed as a pair for a given demodulation technique, and wherein the step of demodulating comprises the steps of

accessing a minimal energy constellation of points expressed as pairs of in-phase and quadrature components representative of the given demodulation technique wherein the number of points equals the number of combinations of output bits in the set and such that each of the points is assigned a unique one of the combinations, and

selecting one of the unique combinations as the output bits corresponding to said each of the complex symbols by comparing the in-phase and quadrature components of said each of the complex symbols to the points in the constellation with reference to a comparison measure to identify said one of the unique combinations.

9. The method as recited in claim 8 further including the steps of

determining the minimal energy constellation of points upon initialization of the method, and

storing the constellation for accessibility by the step of demodulating.

10. The method as recited in claim 9 wherein the given demodulation technique is based upon M-level Quadrature Amplitude Modulation (M-QAM) and the step of determining includes the steps of

defining a set of constellation points for the M-QAM constellation as S_M,

labeling, for the 4-QAM constellation, the point in S₄ having x and y coordinates as P₀→

(x,y), and

labeling the other three points in a counter-clockwise direction to complete the 4-QAM constellation as P₁→

(−

x,y), P₂→

(−

x,−

y), and P₃→

(x,−

y).

11. The method as recited in claim 10 wherein the step of determining further includes, after the second step of labeling, the step of assigning codes to the 4-QAM constellation points based on a Gray code assignment.

12. The method as recited in claim 10 wherein the step of determining further includes, after the second step of labeling, the steps of

iteratively labeling constellation points for 8-QAM and higher by defining the next point P_k→

(x,y) in S_M not already in S<sub>M−

1</sub> and determining the lowest energy point x²+y² not in S<sub>M−

1</sub> using the following rules if two or more points have equal energy;

Rule 1—

if the sums (x+y) for the points are equal, choose the point with the smallest y value;

Rule 2—

if the sums are different, choose the point with the smallest max {x,y},

choosing the three points associated with P_k as P_k+1→

(−

x,y), P_k+2→

(−

x,−

y), and P_k+3→

(x,−

y), and

repeating the iteratively labeling and choosing steps until there are M/4 points in S_M.

13. The method as recited in claim 12 wherein the step of determining further includes the step of assigning codes to the constellation points based on a Gray code assignment whenever feasible.

14. A method for communicating a sequence of input bits from a transmitter over a wireless channel to a receiver to produce a sequence of output bits comprising the steps of

converting the sequence of input bits into a corresponding set of input symbols wherein each of the input symbols represents a unique plurality of the input bits,

modulating each of the input symbols to produce a corresponding set of complex symbols,

computing the inverse Discrete Fourier Transform of the set of complex symbols to produce a transformed set of symbols,

augmenting the transformed set of symbols with cyclic prefix symbols determined with reference to the transformed set to produce a set of output symbols, and

converting the set of output symbols to a serial stream of output bits,

filtering the output bits with to suppress intersymbol interference,

propagating the output bits as a radio frequency signal over the wireless channel, the radio frequency signal including synchronization and timing information,

processing the radio frequency signal to produce a received signal,

recovering the synchronization information and recovering timing information from the received signal,

processing the received signal using the recovered synchronization information to produce a recovered signal,

sampling the recovered signal using the recovered timing information to produce a stream of sampled complex symbols,

removing the cyclic prefix symbols from the sampled complex symbols to produce a reduced set of complex symbols,

computing the Discrete Fourier transform of the reduced set of complex symbols to produce a set of detected complex symbols, and

demodulating the detected complex symbols to generate the sequence of output bits.

15. The method as recited in claim 14 wherein each of the complex symbols has an in-phase component and a quadrature component expressed as a pair for a given modulation technique, and wherein the step of modulating comprises the steps of

accessing a minimal energy constellation of points expressed as pairs of in-phase and quadrature components representative of the given modulation technique wherein the number of points equals the number of combinations of input bits in any of the input symbols and such that each of the points is assigned a unique one of the combinations, and

selecting the in-phase and quadrature components of one of the points for each of the input symbols as the corresponding one of the complex symbols.

16. The method as recited in claim 15 further including the steps of

determining the minimal energy constellation of points upon initialization of the method, and

storing the constellation for accessibility by the step of modulating.

17. The method as recited in claim 14 wherein the given modulation technique is M-level Quadrature Amplitude Modulation (M-QAM) and the step of determining includes the steps of

defining a set of constellation points for the M-QAM constellation as S_M, labeling, for the 4-QAM constellation, the point in S₄ having x and y coordinates as P₀→

(x,y), and

labeling the other three points in a counter-clockwise direction to complete the 4-QAM constellation as P₁→

(−

x,y), P₂→

(−

x,−

y), and P₃→

(x,−

y).

18. The method as recited in claim 17 wherein the step of determining further includes, after the second step of labeling, the step of assigning codes to the 4-QAM constellation points based on a Gray code assignment.

19. The method as recited in claim 17 wherein the step of determining further includes, after the second step of labeling, the steps of

iteratively labeling constellation points for 8-QAM and higher by defining the next point P_k→

(x,y) in S_M not already in S<sub>M−

1</sub> and determining the lowest energy point x²+y² not in S<sub>M−

1</sub> using the following rules if two or more points have equal energy;

Rule 1—

if the sums (x+y) for the points are equal, choose the point with the smallest y value;

Rule 2—

if the sums are different, choose the point with the smallest max {x,y},

choosing the three points associated with P_k as P_k+1→

(−

x,y), P_k+2→

(−

x,−

y), and P_k+3→

(x,−

y), and

repeating the iteratively labeling and choosing steps until there are M/4 points in S_M.

20. The method as recited in claim 19 wherein the step of determining further includes the step of assigning codes to the constellation points based on a Gray code assignment whenever feasible.

21. The method as recited in claim 14 wherein each of the complex symbols in the reduced set has an in-phase component and a quadrature component expressed as a pair for a given demodulation technique, and wherein the step of demodulating comprises the steps of

accessing a minimal energy constellation of points expressed as pairs of in-phase and quadrature components representative of the given demodulation technique wherein the number of points equals the number of combinations of output bits in the set and such that each of the points is assigned a unique one of the combinations, and

selecting one of the unique combinations as the output bits corresponding to said each of the complex symbols by comparing the in-phase and quadrature components of said each of the complex symbols to the points in the constellation with reference to a comparison measure to identify said one of the unique combinations.

22. The method as recited in claim 21 further including the steps of

determining the minimal energy constellation of points upon initialization of the method, and

storing the constellation for accessibility by the step of demodulating.

23. The method as recited in claim 22 wherein the given demodulation technique is based upon M-level Quadrature Amplitude Modulation (N4-QAM) and the step of determining includes the steps of

defining a set of constellation points for the M-QAM constellation as S_M,

labeling, for the 4-QAM constellation, the point in S₄ having x and y coordinates as P₀→

(x,y), and

labeling the other three points in a counter-clockwise direction to complete the 4-QAM constellation as P₁→

(−

x,y), P₂→

(−

x,−

y), and P₃→

(x,−

y).

24. The method as recited in claim 23 wherein the step of determining further includes, after the second step of labeling, the step of assigning codes to the 4-QAM constellation points based on a Gray code assignment.

25. The method as recited in claim 23 wherein the step of determining further includes, after the second step of labeling, the steps of

iteratively labeling constellation points for 8-QAM and higher by defining the next point P_k→

(x,y) in S_M not already in S<sub>M−

1</sub> and determining the lowest energy point x²+y² not in S<sub>M−

1</sub> using the following rules if two or more points have equal energy;

Rule 1—

if the sums (x+y) for the points are equal, choose the point with the smallest y value;

Rule 2—

if the sums are different, choose the point with the smallest max {x,y}, choosing the three points associated with P_k as P_k→

(−

x,y), P_k+2→

(−

x,−

y), and P_k+3→

(x,−

y), and

repeating the iteratively labeling and choosing steps until there are M/4 points in S_M.

26. The method as recited in claim 25 wherein the step of determining further includes the step of assigning codes to the constellation points based on a Gray code assignment whenever feasible.

27. A method for propagating a sequence of input bits over a wireless channel from a transmitter to a receiver, the method comprising the steps of

converting the sequence of input bits into a set of input symbols wherein each of the input symbols represents a unique plurality of the input bits,

modulating each of the input symbols to produce a corresponding set of complex symbols,

augmenting the set of complex symbols with energy-adjusting symbols to produce an augmented set of complex symbols,

computing the inverse Discrete Fourier Transform of the augmented set to produce a transformed set of symbols,

modifying the transformed set of symbols with reference to the energy in the transformed set of symbols,

augmenting the transformed set with cyclic prefix symbols determined with reference to the transformed set to produce a set of output symbols,

converting the set of output symbols to a serial stream of output bits,

filtering the output bits with to suppress intersymbol interference, and

propagating the output bits as a radio frequency signal at a given carrier frequency over the wireless channel from the transmitter,

receiving the radio frequency signal on a plurality of parallel paths in the receiver, the step of receiving for each of the paths including the steps of

recovering carrier frequency synchronization information and recovering complex symbol timing information from the radio frequency signal,

processing the radio frequency signal using the recovered carrier frequency synchronization and the recovered timing information to produce a stream of recovered complex symbols from the input symbols in the radio frequency signal,

removing the cyclic prefix symbols from the recovered complex symbols to produce a reduced set of complex symbols,

computing the Discrete Fourier transform of the reduced set of complex symbols to produce a set of detected complex symbols, and

computing an estimator indicative of the quality of the set of detected complex symbols,

selecting the detected complex symbols from one of the paths based upon its corresponding estimator, and

demodulating the selected detected complex symbols to generate the output set of bits.

28. The method as recited in claim 27 wherein each of the complex symbols has an in-phase component and a quadrature component expressed as a pair for a given modulation technique, and wherein the step of modulating comprises the steps of

accessing a minimal energy constellation of points expressed as pairs of in-phase and quadrature components representative of the given modulation technique wherein the number of points equals the number of combinations of input bits in any of the input symbols and such that each of the points is assigned a unique one of the combinations, and

selecting the in-phase and quadrature components of one of the points for each of the input symbols as the corresponding one of the complex symbols.

29. The method as recited in claim 28 further including the steps of

determining the minimal energy constellation of points upon initialization of the method, and

storing the constellation for accessibility by the step of modulating.

30. The method as recited in claim 29 wherein the given modulation technique is M-level Quadrature Amplitude Modulation (M-QAM) and the step of determining includes the steps of

defining a set of constellation points for the M-QAM constellation as S_M,

labeling, for the 4-QAM constellation, the point in S₄ having x and y coordinates as P₀→

(x,y), and

labeling the other three points in a counter-clockwise direction to complete the 4-QAM constellation as P₁→

(−

x,y), P₂→

(−

x,−

y), and P₃→

(x,−

y).

31. The method as recited in claim 30 wherein the step of determining further includes, after the second step of labeling, the step of assigning codes to the 4-QAM constellation points based on a Gray code assignment.

32. The method as recited in claim 30 wherein the step of determining further includes, after the second step of labeling, the steps of

iteratively labeling constellation points for 8-QAM and higher by defining the next point P_k→

(x,y) in S_M not already in S<sub>M−

1</sub> and determining the lowest energy point x²+y not in S<sub>M−

1</sub> using the following rules if two or more points have equal energy;

Rule 1—

if the sums (x+y) for the points are equal, choose the point with the smallest y value;

Rule 2—

if the sums are different, choose the point with the smallest max {x,y},

choosing the three points associated with P_k as P_k+1→

(−

x,y), P_k+2→

(−

x,−

y), and P_k+3→

(x,−

y), and

repeating the iteratively labeling and choosing steps until there are M/4 points in S_M.

33. The method as recited in claim 32 wherein the step of determining further includes the step of assigning codes to the constellation points based on a Gray code assignment whenever feasible.

34. The method as recited in claim 27 wherein each of the complex symbols in the reduced set has an in-phase component and a quadrature component expressed as a pair for a given demodulation technique, and wherein the step of demodulating comprises the steps of

accessing a minimal energy constellation of points expressed as pairs of in-phase and quadrature components representative of the given demodulation technique wherein the number of points equals the number of combinations of output bits in the set and such that each of the points is assigned a unique one of the combinations, and

selecting one of the unique combinations as the output bits corresponding to said each of the complex symbols by comparing the in-phase and quadrature components of said each of the complex symbols to the points in the constellation with reference to a comparison measure to identify said one of the unique combinations.

35. The method as recited in claim 34 further including the steps of

determining the minimal energy constellation of points upon initialization of the method, and

storing the constellation for accessibility by the step of demodulating.

36. The method as recited in claim 35 wherein the given demodulation technique is based upon M-level Quadrature Amplitude Modulation (M-QAM) and the step of determining includes the steps of

defining a set of constellation points for the M-QAM constellation as S_M,

labeling, for the 4-QAM constellation, the point in S₄ having x and y coordinates as P₀→

(x,y), and

labeling the other three points in a counter-clockwise direction to complete the 4-QAM constellation as P₁→

(−

x,y), P₂→

(−

x,−

y), and P₃→

(x,−

y).

37. The method as recited in claim 36 wherein the step of determining further includes, after the second step of labeling, the step of assigning codes to the 4-QAM constellation points based on a Gray code assignment.

38. The method as recited in claim 36 wherein the step of determining further includes, after the second step of labeling, the steps of

iteratively labeling constellation points for 8-QAM and higher by defining the next point P_k→

(x,y) in S_M not already in S<sub>M−

1</sub> and determining the lowest energy point x²+y² not in S<sub>M−

1</sub> using the following rules if two or more points have equal energy;

Rule 1—

if the sums (x+y) for the points are equal, choose the point with the smallest y value;

Rule 2—

if the sums are different, choose the point with the smallest max {x,y},

choosing the three points associated with P_k as P_k+1→

(−

x,y), P_k+2→

(−

x,−

y), and P_k+3→

(x,−

y), and

repeating the iteratively labeling and choosing steps until there are M/4 points in S_M.

39. The method as recited in claim 38 wherein the step of determining further includes the step of assigning codes to the constellation points based on a Gray code assignment whenever feasible.

40. A method for communicating a sequence of input bits as a time-division multiple-access frame from a transmitter over a wireless channel to produce an outgoing stream of bits corresponding to the sequence of input bits in a receiver, the method comprising the steps of

converting the sequence of input bits into a corresponding set of input symbols wherein each of the input symbols represents a unique plurality of the input bits,

partitioning the time-division multiple-access frame into a plurality of slots each having a prescribed bandwidth and assigning one of the slots to the sequence of input bits,

subdividing the prescribed bandwidth of the assigned slot into a plurality of orthogonal frequency division multiplexed subchannels each conveying a corresponding one of the input symbols from the set,

propagating the frame over the wireless channel,

processing the frame received over the wireless channel to detect the input symbols each corresponding to one of the ODFM channels,

transforming the OFDM channels to generate a set of transformed complex symbols from the incoming symbols, and

processing the transformed complex symbols to generate the outgoing stream of output bits.

41. A system for communicating a sequence of input bits over a wireless channel to produce a sequence of output bits corresponding to the sequence of input bits, the system comprising

a transmitter including

a converter for converting the sequence of input bits into a corresponding set of input symbols wherein each of the input symbols represents a unique plurality of the input bits,

a modulator for modulating each of the input symbols to produce a corresponding set of complex symbols,

a transform processor for computing the inverse Discrete Fourier Transform of the set of complex symbols to produce a transformed set of symbols,

means for augmenting the transformed set of symbols with cyclic prefix symbols determined with reference to the transformed set to produce a set of output symbols,

an output processor for processing the set of output symbols to generate a radio frequency signal at a given carrier frequency, the radio frequency signal including carrier synchronization information and complex symbol timing information to recover the output symbols,

means for propagating the radio frequency signal over the wireless channel,

the receiver including

means for recovering the carrier frequency synchronization information and recovering the complex symbol timing information from the radio frequency signal,

a processor for processing the radio frequency signal using the recovered carrier frequency synchronization and the recovered timing information to produce a stream of recovered complex symbols,

a cyclic device for removing the cyclic prefix symbols from the recovered complex symbols to produce a reduced set of complex symbols,

a processor for computing the Discrete Fourier transform of the reduced set of complex symbols to produce a set of detected complex symbols, and

a demodulator for demodulating the detected complex symbols to generate the sequence of output bits.