Efficient multipath centroid tracking circuit for a code division multiple access (CDMA) system

• US 6,381,264 B1
• Filed: 03/03/1999
• Issued: 04/30/2002
• Est. Priority Date: 06/30/1995
• Status: Expired due to Term

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Ozluturk, Fatih, Lomp, Gary
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): PHU, PHUONG M
• Application Number:
  US09/261,689
• Time in Patent Office: 1,154 Days
• Field of Search: 375/149, 375/145, 375/134, 375/137, 375/367, 375/148, 375/362, 370/515, 370/516, 370/517
• US Class Current: 375/149
• CPC Class Codes: G06F 13/374 using a self-select method with individual priority code comparator
• CPC Class Codes: H03H 17/0226 comprising look-up tables
• CPC Class Codes: H03H 17/06 Non-recursive filters
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/70753 Partial phase search
• CPC Class Codes: H04B 1/70754 Setting of search window, i.e. range of code offsets to be searched H04B1/70758 takes precedence
• CPC Class Codes: H04B 1/70755 Setting of lock conditions, e.g. threshold
• CPC Class Codes: H04B 1/70758 Multimode search, i.e. using multiple search strategies
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 1/708 Parallel implementation
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/7093 Matched filter type
• CPC Class Codes: H04B 1/711 the interference being multi-path interference
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 1/712 Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04B 2201/70703 using multiple or variable rates
• CPC Class Codes: H04B 2201/70707 : Efficiency-related aspects
• CPC Class Codes: H04B 2201/7071 : with dynamic control of receiver resources
• CPC Class Codes: H04B 7/2628 : using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] H04B7/2618 takes precedence
• CPC Class Codes: H04B 7/2637 : for logical channel control
• CPC Class Codes: H04B 7/264 : for data rate control
• CPC Class Codes: H04J 13/00 : Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04J 13/004 : Orthogonal
• CPC Class Codes: H04J 13/0048 : Walsh
• CPC Class Codes: H04J 13/0077 : Multicode, e.g. multiple codes assigned to one user
• CPC Class Codes: H04J 13/10 : Code generation
• CPC Class Codes: H04J 13/107 : by concatenation
• CPC Class Codes: H04J 13/12 : Generation of orthogonal codes
• CPC Class Codes: H04J 13/16 : Code allocation
• CPC Class Codes: H04J 2013/0037 : Multilevel codes
• CPC Class Codes: H04L 1/0001 : Systems modifying transmission characteristics according to link quality, e.g. power backoff adaptive data allocation for multicarrier modulation H04L5/0044; controlling transmission power for radio systems H04W52/04
• CPC Class Codes: H04L 1/004 : by using forward error control H04L1/0618 takes precedence; coding, decoding or code conversion, for error detection or correction H03M13/00
• CPC Class Codes: H04L 1/0042 : Encoding specially adapted to other signal generation operation, e.g. in order to reduce transmit distortions, jitter, or to improve signal shape H04L1/0067 takes precedence
• CPC Class Codes: H04L 1/0047 : Decoding adapted to other signal detection operation in conjunction with sequence estimation or equalization H04L25/03286
• CPC Class Codes: H04L 1/0054 : Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
• CPC Class Codes: H04L 1/0059 : Convolutional codes
• CPC Class Codes: H04L 2027/003 : at baseband only
• CPC Class Codes: H04L 2027/0053 : Closed loops
• CPC Class Codes: H04L 25/0212 : of impulse response
• CPC Class Codes: H04L 27/206 : using a pair of orthogonal carriers, e.g. quadrature carriers
• CPC Class Codes: H04L 27/2332 : using a non-coherent carrier
• CPC Class Codes: H04L 5/1446 : of transmission speed
• CPC Class Codes: H04N 1/00912 : Arrangements for controlling a still picture apparatus or components thereof not otherwise provided for
• CPC Class Codes: H04N 1/3333 : during transmission, input or output of the picture signal; within a single document or page
• CPC Class Codes: H04N 2201/3335 : Speed or rate
• CPC Class Codes: H04W 52/04 : TPC
• CPC Class Codes: H04W 52/08 : Closed loop power control
• CPC Class Codes: H04W 52/143 : Downlink power control
• CPC Class Codes: H04W 52/146 : Uplink power control
• CPC Class Codes: H04W 52/24 : using SIR [Signal to Interference Ratio] or other wireless path parameters
• CPC Class Codes: H04W 52/241 : taking into account channel quality metrics, e.g. SIR, SNR, CIR, Eb/lo
• CPC Class Codes: H04W 52/245 : taking into account received signal strength
• CPC Class Codes: H04W 52/247 : where the output power of a terminal is based on a path parameter sent by another terminal
• CPC Class Codes: H04W 52/26 : using transmission rate or quality of service QoS [Quality of Service]
• CPC Class Codes: H04W 52/262 : taking into account adaptive modulation and coding [AMC] scheme AMC per se H04L1/0001
• CPC Class Codes: H04W 52/322 : Power control of broadcast channels
• CPC Class Codes: H04W 52/325 : Power control of control or pilot channels
• CPC Class Codes: H04W 52/343 : taking into account loading or congestion level
• CPC Class Codes: H04W 52/346 : distributing total power among users or channels
• CPC Class Codes: H04W 52/36 : with a discrete range or set of values, e.g. step size, ramping or offsets
• CPC Class Codes: H04W 52/367 : Power values between minimum and maximum limits, e.g. dynamic range
• CPC Class Codes: H04W 52/44 : in connection with interruption of transmission
• CPC Class Codes: H04W 52/50 : at the moment of starting communication in a multiple access environment
• CPC Class Codes: H04W 52/52 : using AGC [Automatic Gain Control] circuits or amplifiers
• CPC Class Codes: H04W 52/54 : Signalisation aspects of the TPC commands, e.g. frame structure
• CPC Class Codes: H04W 52/60 : using different transmission rates for TPC commands
• CPC Class Codes: Y02D 10/00 : Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

A multiple access, spread-spectrum communication tracking system includes apparatus which tracks a centroid of a transmitted code-division multiplexed (CDM) code sequence that is contaminated with multipath distortion. The apparatus includes an analog to digital converter which digitally samples the spread-spectrum channel signal to produce a sequence of sample values. The sample values are divided into a set of even-numbered sample values which correspond to early multipath signal components and the set of odd sample number values which correspond to the multipath signal components. The centroid tracking receiver generates a plurality of local code sequences, each of which is a code phase-shifted version of the transmitted code sequence. The centroid tracking receiver correlates each of the locally generated code sequences with the odd and even numbered sample values, respectively, to produce a group of early despread multipath signals and a group of late despread multipath signals. The group of early despread multipath signals are weighted and processed to produce an early tracking value, and the group of late despread multipath signals are weighted and processed to produce a late tracking value. The difference between the early tracking value and the late tracking value is calculated to produce an error signal value. Finally, the centroid tracking system adjusts the code phase of each of the locally generated code sequences to minimize the error signal value.

Claims

1. A method for tracking multipath components of a spread spectrum signal, the spread spectrum signal having an associated chip code sequence, the method comprising:

receiving multipath components of the spread spectrum signal;

despreading a first and a second plurality of multipath components about a center code phase, the first plurality being a sequence of multipath components prior to the center code phase and the second plurality being a sequence of multipath components after the center code phase;

determining a first combined energy of the despread first plurality of multipath components;

determining a second combined energy of the despread second plurality of multipath components;

calculating a tracking delay based on a difference of the first and second combined energies;

adjusting the center code phase by said tracking delay whereby the center phase is not adjusted if the first combined energy equals the second combined energy; and

weighting the first and the second plurality of multipath components prior to determining the first and the second combined energy such that multipath components of the first and the second plurality of multipath components further from the center code phase are provided a higher weighting value and the first combined energy is of the weighted despread first plurality of multipath components and the second combined energy is of the weighted despread second plurality of multipath components.

2. The method of claim 1, wherein the first and the second plurality of multipath components includes the received multipath components of the spread-spectrum signal for each chip of a continuous sequence of chips from the center code phase.

3. The method of claim 1 wherein the weighting values associated with each multipath component of the first and the second plurality of multipath components is based on squaring a difference between a delay associated with the respective multipath component and the center code phase.

4. The method of claim 1 wherein the first and the second plurality of multipath components includes the received multipath components of the spread-spectrum signal for each half chip of a continuous sequence of chips from the center code phase.

5. A device for tracking multipath components of a spread-spectrum signal, the spread-spectrum signal having an associated chip code sequence, the device comprising:

means for receiving multipath components of the spread-spectrum signal;

means for despreading a first and a second plurality of multipath components about a center code phase, the first plurality being a sequence of multipath components prior to the center code phase and the second plurality being a sequence of multipath components after the center code phase;

means for determining a first combined energy of the despread first plurality of multipath components;

means for determining a second combined energy of the despread second plurality of multipath components;

means for calculating a tracking delay based on a difference of the first and the second combined energies;

means for adjusting the center code phase by said tracking delay whereby the center code phase is not adjusted if the first combined energy equals the second combined energy; and

means for weighting the first and the second plurality of multipath components prior to determining the first and the second combined energy such that multipath components of the first and the second plurality of multipath components further from the center code phase are provided a higher weighting value and the first combined energy is of the weighted despread first plurality of multipath components and the second combined energy is of the weighted despread second plurality of multipath components.

6. The device of claim 5 wherein the first and the second plurality of multipath components includes the received multipath components of the spread-spectrum signal for each chip of a continuous sequence of chips from the center code phase.

7. The device of claim 5 wherein said weighting means weights each multipath component of the first and the second plurality of multipath components by a weight based on a square of a difference between a delay associated with the respective multipath component and the center code phase.

8. The device of claim 5 wherein the first and the second plurality of multipath components includes the multipath components of the spread-spectrum signal for each chip of a continuous sequence of chips from the center code phase.

9. A device for tracking multipath components of a spread-spectrum signal, the spread-spectrum signal having an associated chip code sequence, the device comprising:

means for receiving multipath components of the spread-spectrum signal;

a first and a second correlation bank for despreading a first and second plurality of multipath components, respectively, the first plurality being a sequence of multipath components prior to a center code phase and the second plurality being a sequence of multipath components after the center code phase;

a first sum and dump bank coupled to a first calculator bank for determining a magnitude associated with each of the first plurality of the multipath components; and

a first summer for adding the magnitudes of the first plurality of multipath components as a first combined energy;

a second sum and dump bank coupled to a second calculator bank for determining a magnitude associated with each of the second plurality of multipath components;

a second summer for adding the magnitudes of the second plurality of multipath components as the second combined energy;

an adder for calculating the difference of the first and the second combined energies as a tracking delay; and

means for adjusting the center code phase by said tracking delay whereby the center code phase is not adjusted if the first combined energy equals the second combined energy.