Multicarrier personal access communication system

• US 6,633,614 B1
• Filed: 12/30/1999
• Issued: 10/14/2003
• 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: Barton, Melbourne, Wong, Kouk-Shoong Daniel
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): CHANG, EDITH M
• Application Number:
  US09/476,466
• Time in Patent Office: 1,384 Days
• Field of Search: 375/264, 375/260, 375/261, 375/202, 375/308, 370/210, 370/18, 370/206, 370/347, 370/204, 725/106, 714/790, 329/304
• US Class Current: 375/264
• 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 system for propagating a sequence of input bits as a wireless channel comprising

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 in the set to produce a corresponding set of complex symbols, each of the complex symbols having an in-phase component and a quadrature component expressed as a pair for a given modulation technique and said modulator including

circuitry for accessing a minimal energy constellation of points expressed as pairs of 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 such that each of the points is assigned a unique one of the combinations, and

a selector for 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,

means for determining the minimal energy constellation points upon intialization of the system,

a storage device for storing the constellation for accessibility by the modulator,

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

circuitry 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, and

a signal processor for processing the set of output symbols to generate the wireless channel signal, and

wherein the given modulation technique is M-level Quadrature Amplitude Modulation (M-QAM) and the means for determining the minimum energy constellation points includes

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

means for labeling, for the 4-QAM constellation, the point S₄ having x and y coordinates as P₀, i.e., P₀→

(−

x,y),

means for labeling the other three points P₁, P₂, and P₃ in a counter clockwise direction to complete the 4-QAM constellation as P₁→

(x,y), P₂→

(−

x,−

y), and P₃→

(x,−

y),

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

(x,y) in S_M not already in S_M−

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},

means for choosing the three points P_k+1, P_k+2, and P_k+3 associated with P_k as P_k+1→

(−

x,y), P_k+2→

(−

x,−

y), and P_k+3→

(x,−

y), and

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

2. The system as recited in claim 1 wherein the means for determining further includes means for assigning codes to the constellation points based on a Gray code assignment whenever feasible.

3. A system for generating a set of output bits representative of a complex input symbol, the complex input symbol having an in-phase component and a quadrature component expressed as a pair for a given demodulation technique based upon M-level Quadrature Amplitude Modulation (M-QAM), the system comprising

a look-up table composed of 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,

a storage device for storing the look-up table,

a selector for identifying 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, and

means for determining the look-up table upon initialization of the system, said means for determining including

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

means for labeling, for the 4-QAM constellation, the point S₄ having x and y coordinates as P₀, i.e., P₀→

(x,y),

means for labeling the other three points P₁, P₂, and P₃ in a counter-clockwise direction to complete the 4-QAM constellation as P₁→

(−

x,y), P₂ (−

x,−

y), and P₃→

(x,−

y),

means for iteratively labeling constellation points for 8-QAM and higher by defining the next point with coordinates P_k, 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 two 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 smallest y value;

Rule 2—

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

means for choosing the three points P_k+1, P_k+2, and P_k+3 associated with P_k as P_k+1→

(−

x,y), P_k+2→

(−

x,−

y), and P_k+3→

(x,−

y), and

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

4. The system as recited in claim 3 wherein the means for determining further includes means for assigning codes to the constellation points based on a Gray code assignment whenever feasible.

5. A method for genemling a complex symbol representative of a set of input bits, the complex symbol having an in-phase component and a quadrature component expressed as a pair for a modulation technique, the method comprising 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 the set and such that each of the points is assigned a unique one of the combinations,

selecting the in-phase and quadrature components of one of the points corresponding to the input bits as the complex output symbol,

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

storing the constellation for accessibility by the step of selecting, and 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 P<sub>0→

(x,y),</sub>

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), and, after the second step of labeling.

assigning codes to the 4-QAM constellation points based on a Gray code assignment,

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

(x,y) in the S_M not already in the S<sub>M−

1</sub> and determining to 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 of (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 at M/4 points in S_M.

6. The method as recited in claim 5 wherein the step of determining further includes the step of assigning codes to the constellation points based on a Gray code assignment whenever feasible.