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

• US 5,912,919 A
• Filed: 06/27/1996
• Issued: 06/15/1999
• 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): Bocure, Tesfaldet
• Application Number:
  US08/669,771
• Time in Patent Office: 1,083 Days
• Field of Search: 375/206, 375/208, 375/207, 375/267, 375/347, 375/362
• 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 a centroid of a plurality of multipath spread-spectrum signals, said plurality of multipath spread-spectrum signals constituting a spread-spectrum channel signal including a transmitted code sequence, the method comprising the steps of:

match filtering and digitally sampling the spread-spectrum channel signal responsive to a clock signal to produce a sequence of sample values including a set of even numbered sample values and a set odd-numbered sample values;

wherein said set of even-numbered sample values define a sequence of early spread-spectrum channel signal samples and said set of odd numbered sample values define a sequence of late spread-spectrum channel signal samples;

generating a plurality of local code sequences, each of said plurality of local code sequences having a code phase and code symbol period, and each being a code phase-shifted version of the transmitted code sequence;

combining each of said plurality of local code sequences with the sequence of early received spread-spectrum channel signal samples to produce a plurality of early despread multipath signals, and combining each of said plurality of local code sequences with the sequence of late received spread-spectrum channel signal samples to produce a plurality of late despread multipath signals;

processing the plurality of early despread multipath signals to produce an early tracking value, and processing the plurality of late despread multipath signals to produce a late tracking value;

determining a difference between the early tracking value and the late tracking value to produce an error signal value; and

adjusting the code phase of each of said plurality of local code sequences responsive to the error signal value so that the energy of the early and late received spread-spectrum channel signal samples is equal.

2. The method of claim 1, wherein the steps of processing the plurality of early despread multipath signals and processing the plurality of late despread multipath signals comprise the steps of:

accumulating said plurality of early despread multipath signals to produce a respective plurality of early signal samples, and accumulating said plurality of late despread multipath signals to produce a respective plurality of late signal samples; and

summing ones of the early signal samples to produce said early tracking value, and summing ones of the late signal samples to produce said late tracking value.

3. The method of claim 2, wherein, prior to the step of summing, the method includes the step of weighting each of said early signal samples and each of said late signal samples with a respective predetermined weighting value.

4. The method of claim 1, wherein the step of adjusting the code phase of each of said plurality of local code sequences includes the steps of increasing each code phase by a first predetermined number of code symbol periods responsive to the error signal value being negative, and decreasing each code phase by a second predetermined number of code symbol periods responsive to the error signal value being positive.

5. The method of claim 1, wherein the step of adjusting the code phase of each of said plurality of local code sequences includes the steps of increasing each code phase by a first predetermined number of code symbol periods responsive to the error signal value being positive, and decreasing each code phase by a second predetermined number of code symbol periods responsive to the error signal value being negative.

6. Apparatus for tracking a centroid of a plurality of multipath spread-spectrum signals, said plurality of multipath spread-spectrum signals constituting a spread-spectrum channel signal including a transmitted code sequence, the apparatus comprising:

means for match filtering the spread-spectrum channel signal;

an analog-to-digital converter, responsive to a clock signal and the match filtered spread-spectrum channel signal to produce a sequence of sample values including a set of even numbered sample values and a set of odd-numbered sample values;

wherein said set of even-numbered sample values define a sequence of early spread-spectrum channel signal samples and said set of odd sample number values define a sequence of late spread-spectrum channel signal samples;

code sequence generating means for generating a plurality of local code sequences, each of said plurality of local code sequences having a code phase and code symbol period, and each being a code phase-shifted version of the transmitted code sequence;

means for combining each of said plurality of local code sequences with the Sequence of early received spread-spectrum channel signal samples to produce a plurality of early despread multipath signals, and for combining each of said plurality of local code sequences with the sequence of late received spread-spectrum channel signal samples to produce a plurality of late despread multipath signals;

means for processing the plurality of early despread multipath signals to produce an early tracking value, and for processing the plurality of late despread multipath signals to produce a late tracking value;

a subtracter which determines the difference between the early tracking value and the late tracking value to produce an error signal value; and

means, coupled to the code phase generating means, for adjusting the code phase of each of said plurality of local code sequences responsive to the error signal value so that the energy of the early and late received spread-spectrum channel signal samples is equal.

7. The apparatus of claim 6, wherein the means for processing the plurality of early despread multipath signals and for processing the plurality of late despread multipath signals comprise:

a first plurality of accumulators which accumulate said plurality of early despread multipath signals to produce a respective plurality of early signal samples, and a second plurality of accumulators which accumulate said plurality of late despread multipath signals to produce a respective plurality of late signal samples; and

a first summing network for summing ones of the early signal samples to produce said early tracking value, and a second summing network for summing ones of the late signal samples to produce said late tracking value.

8. The apparatus of claim 7, further including a plurality of signal scalers which multiply each of said early signal samples and each of said late signal samples by a respective predetermined weighting value and which apply the weighted early and late signal samples to the respective first and second summing networks.