Code sequence generator in a CDMA modem

• US 6,272,168 B1
• Filed: 03/04/1998
• Issued: 08/07/2001
• 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, Silverberg, Avi
• Primary Examiner(s): Le, Amanda T.
• Application Number:
  US09/034,855
• Time in Patent Office: 1,252 Days
• Field of Search: 375/206-208, 375/210, 375/222, 375/342, 375/343, 375/354, 375/362, 375/364, 375/367, 370/320, 370/335, 370/342, 708/252
• US Class Current: 375/222
• 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 CDMA modem includes a modem transmitter having: a code generator which provides an associated pilot code signal and which generates a plurality of message code signals: a spreading circuit which produces a spread-spectrum message signal by combining each of the information signals with a respective one of the message code signals; and a global pilot code generator that provides a global pilot code signal to which the message code signals are synchronized. The CDMA modem also includes a modem receiver having an associated pilot code generator and a group of associated pilot code correlators for correlating code-phase delayed versions of the associated pilot signal with a receive CDM signal to produce a despread associated pilot signal. The code phase of the associated pilot signal is changed responsive to an acquisition signal value until a pilot signal is received. The associated pilot code tracking logic adjusts the associated pilot code signal in phase responsive to the acquisition signal so that the signal power level of the despread associated pilot code signal is maximized. Finally, the CDMA modem receiver includes a group of message signal acquisition circuits, each including a plurality of receive message signal correlators which correlate respective local received message code signal to the CDM signal to produce a respective despread received message signal.

Claims

1. A Code Division Multiple Access (CDMA) modem that transmits and receives telecommunication signals over a transmit and a receive channel having respective first and second pilot code signals, the second pilot code signal being synchronous with the first pilot code signal and the telecommunication signals including information signals, the modem comprising

a modem transmitter having:

a) code generation means comprising a first pilot code means for providing the first pilot code signal selected from a plurality of distinct pilot code signals and a message means for generating a plurality of distinct transmit message code signals, related to and synchronous with the first pilot code signal;

b) spreading means coupled to the message means for combining each of the information signals, with a respective one of the plurality of transmit message code signals to generate a plurality of spread-spectrum processed message signals comprising a transmit Code Division Multiplex (CDM) signal for transmission over the transmit channel, and the first pilot signal wherein each of the plurality of transmit message code signals is synchronous with the pilot code signal; and

a modem receiver having;

a) local code generation means comprising a local second pilot code means for providing a local version of the second pilot code signal related to the first pilot code signal and a local message code means for generating a plurality of local receive message code signals related to the second pilot code signal, the second pilot code means being synchronous with the local message code means;

b) a pilot code acquisition means for acquiring the second pilot code signal comprising a pilot vector correlator for estimating a channel impulse response associated with the second pilot code signal wherein the channel impulse response estimate is determined by estimating a complex channel response affecting each multipath component of the second pilot code signal, and for correlating a plurality of phase-delayed versions of the second pilot code signal with a received CDM signal from the receive channel using the channel impulse response estimate to produce a despread second pilot signal, the code phase of the second pilot code signal being changed responsive to an acquisition signal; and

detection means for detecting the presence of the despread associated pilot signal to produce an acquisition signal, the acquisition signal indicating a degree of synchronization between the second pilot code signal, the received second pilot code signal and the first pilot code signal;

c) a second pilot code tracking means including means for adjusting the local second pilot code signal in phase responsive to the acquisition signal in a sense which tends to increase the level of the despread second pilot signal; and

d) message signal acquisition means for providing a plurality of despread receive message signals, the message signal acquisition means correlating the plurality of local receive message code signals with the received CDM signal using the channel response estimate of the second pilot code signal to produce the plurality of despread receive message signals.

2. The CDMA modem as recited in claim 1, wherein the telecommunication signals further include connection control signals and the spreading means of the modem transmitter further combines the call control signals with a respective one of the plurality of message code signals to form a call control channel.

3. The CDMA modem as recited in claim 2 wherein the call control signals include a user identification signal which identifies the user for the respective information signal and a message type signal which indicates a type and an information rate for the information signal.

4. The CDMA modem as recited in claim 1, wherein the pilot vector correlator of the pilot code acquisition means further includes:

A) delay means for generating the plurality of phase-delayed versions of the second pilot code signal and a plurality of second pilot code-phase delayed correlation means each correlating a respective one of the plurality of phase-delayed versions of the second pilot code signal with the received CDM signal to produce a plurality of despread multipath pilot signals, and each providing a respective multipath weight signal corresponding to a respective multipath carrier of a respective one of the despread multipath pilot signals; and

B) a pilot adaptive matched filter including a plurality of signal weighting means for scaling, in magnitude, and rotating, in phase, the respective despread multipath pilot signals and each responsive to the respective multipath weighting signal, the plurality of signal weighting means providing a plurality of weighted despread multipath pilot signals, and a summing means for summing the plurality of weighted despread multipath pilot signals to form a despread second pilot signal; and

wherein the detection means, being coupled to the pilot vector correlator, produces the acquisition signal having a magnitude which is proportional to the despread second pilot code signal in signal energy, the magnitude of the acquisition signal indicating a degree of synchronization between the associated pilot code signal and the first pilot code signal; and

the second pilot code tracking means includes means for adjusting the second pilot code signal in code phase, responsive to the acquisition signal in a sense which tends to increase in signal energy the despread second code pilot signal; and

wherein the message signal acquisition means includes;

A) a plurality of receive message signal correlators for correlating the receive message code signals with the CDM signal to produce a plurality of despread multipath receive message signals respectively;

B) a message adaptive matched filter including a plurality of signal weighting means for aligning the respective despread multipath receive message signals in carrier phase responsive to the multipath weighting signals, the plurality of signal weighting means providing a plurality of weighted despread multipath receive message signals, and a summing means for summing the plurality of weighted despread multipath receive message signals to form a despread receive message signal.

5. The CDMA modem as recited in claim 3, wherein the pilot vector correlator further comprises:

a phase locked loop (PLL) which measures a carrier phase error of each respective despread multipath pilot signal and produces a composite carrier phase error signal;

wherein the phase error signal and each one of the plurality of despread multipath pilot signals and the respective multipath signal weighting value are applied to a respective one of a plurality of multipliers, and each despread multipath pilot signal is multiplied by the respective weighting value and the phase error signal to produce one scaled and phase rotated second pilot signal component of a plurality of scaled and phase rotated pilot signal components having substantially equal carrier phases.

6. The CDMA modem as recited in claim 1, wherein:

the message signal acquisition means includes an adaptive matched filter (AMF) means for collecting signal power of a spread data channel of each of the plurality of receive message signals in the received CDM signal having a plurality of multipath signal components, each of said multipath signal components having a carrier phase, and the received CDM signal includes at least one spread data channel employing a second predetermined spreading code sequence corresponding to one of the plurality of local receive message code signals, and the spread data channel is data-modulated;

the pilot vector correlator means provides a plurality of multipath signal weighting values, each weighting value being determined from the respective one of the plurality of phase-delayed versions of the second pilot code correlated with the received CDM signal, and each multipath signal weighting value corresponding to a respective multipath signal carrier of the respective received multipath signal component;

the local code generation means generates a plurality of code phase-shifted versions of the one of the plurality of local receive message code signals; and

the data AMF means, coupled to receive the spread signal, provides a data value determined from one of the despread receive message signals from the received CDM signal, the data AMF means comprising;

a) a plurality of spreading code correlators, each spreading code correlator correlating a respective one of the code phase-shifted versions of the one of the plurality of local receive message code signals with the received CDM signal to produce a respective despread multipath data signal component having a carrier phase value;

b) weighting means for scaling the data value and for aligning the carrier phase value of the despread multipath data responsive to the respective multipath weighting value; and

c) first combining means for combining each one of the scaled and aligned data signal components to produce the data value.

7. The CDMA modem as recited in claim 6, wherein:

a) each of the plurality of spreading code correlators of the data AMF means further includes multiplication means for multiplying the received CDM signal with a respective one of the code phase-shifted versions of the one of the plurality of local receive message code signals to produce a correlated signal value and accumulation means for accumulating the correlated signal value for a predetermined period to produce a despread multipath data signal component having a carrier phase which corresponds to the carrier signal phase of the respective received multipath signal component; and

b) the aligning means comprises a plurality of multipliers, each multiplier multiplying a respective one of the despread multipath data signal components with a respective one of the multipath signal weighting values, and each multiplier producing one weighted data signal component of a plurality of weighted data signal components.

8. The adaptive matched filter (AMF) apparatus of claim 6, wherein the pilot vector correlator means further comprises:

local pilot code sequence generator means for generating a plurality of local code sequences, each of the code sequences being a code phase-shifted version of the pilot spreading code sequence;

a plurality of pilot spreading code correlators, each pilot spreading code correlator correlating a respective one of the local code sequences with the spread signal, each spreading code correlator comprising multiplication means for multiplying the spread signal with the respective one of the local code sequences to produce a correlated pilot signal value and accumulator means for accumulating the correlated pilot signal value for a predetermined period to produce a despread multipath pilot signal component with a carrier signal phase;

wherein each one of the plurality of despread multipath pilot signal components is applied to a respective one of a plurality of low pass filters to produce a multipath signal weighting value corresponding to the carrier signal phase of the respective received multipath signal component;

each one of the plurality of despread multipath pilot signal components and the respective multipath signal weighting value is applied to a respective one of a plurality of multipliers; and

each multipath pilot signal component is multiplied by the respective multipath signal weighting value to produce one scaled and phase rotated pilot signal component of a plurality of scaled and phase rotated pilot signal components having substantially equal carrier phases; and

second combining means for combining the plurality of weighted pilot signal components to produce a pilot data value.

9. The CDMA modem as recited in claim 1, wherein the respective code generation means of the modem transmitter and of the modem receiver each generates the respective pilot code signal from a master spreading code sequence and the plurality of message code signals from a plurality of spreading code sequences having relatively low mutual cross correlation, and having a predetermined mutual code phase relationship, the code sequence generator apparatus comprising:

clock generator means for generating a clock signal;

a linear feedback shift register (LFSR), responsive to the clock signal and having a plurality of stages including a first stage and a last stage, each stage defining a respective tap, each tap producing a tap signal;

wherein a predetermined group of the tap signals including the tap signal of the last stage are applied to logic circuitry which combines the tap signals to produce a feedback spreading-code signal, said feedback spreading-code signal being applied as an input signal to the first stage of the LFSR;

first memory means for storing a plurality of spreading-code seeds, each spreading-code seed comprising a set of spreading-code sequence bit values, and said first memory being connected to the LFSR and being responsive to a load signal for transferring each one of a predetermined set of the spreading-code sequence bit values of a selected one of a plurality of spreading-code seeds into a respective one of the shift register stages of the LSFR;

code generator controller means for selecting one of the plurality of spreading-code seeds to determine the plurality of spreading code sequences and for providing the load signal indicating said one spreading-code seed;

wherein said LSFR is responsive to the clock signal to sequentially transfer each respective tap signal from one stage to the next stage, from the first stage to the last stage and for transferring the feedback spreading-code value to the first stage, and each successive one of the tap values of the last stage defines the master spreading code sequence;

second memory means being responsive to the clock signal for providing a repetitive even code sequence, said even code sequence having relatively low cross correlation with the master spreading sequence and having an even number of chip spreading values;

a plurality of cascade connected feedforward means, coupled to receive the master spreading code sequence, for providing a plurality of code sequences, each code sequence being a distinct spreading code sequence of said plurality of spreading code sequences, said feedforward means being responsive to the clock signal, to provide a plurality of spreading code sequences; and

a plurality code sequence combining means, each code sequence combining means for combining a respective spreading code sequence with said even code sequence to produce a plurality of relatively long spreading codes.

10. The CDMA modem as recited in claim 9, wherein the plurality of cascade connected feedforward means of each code sequence generator includes:

receiving means for receiving the master spreading sequence;

a feedforward circuit having a plurality of cascade connected feedforward logic sections, each logic section defining a tap which provides one of the plurality of spreading code sequences, including a first feedforward logic section and a last feedforward logic section and connected sequentially from the first feedforward logic section to the last feedforward logic section, each feedforward logic section comprising a single delay element having an input terminal which receives an input signal and an output terminal which provides an output signal, and logic combining means for logically combining the input signal with the output signal to produce the respective spreading code sequence.

11. The CDMA modem as recited in claim 10, wherein the code sequence combining means comprises an EXCLUSIVE-OR logic circuit.

12. The CDMA modem as recited in claim 10, wherein the logic combining means comprises an EXCLUSIVE-OR logic circuit for performing modulo-2 addition.

13. The CDMA modem as recited in claim 1, wherein the second pilot code tracking means includes a centroid tracking circuit which tracks a centroid of a plurality of multipath spread-spectrum signals, the plurality of multipath spread-spectrum signals constituting the received CDM signal including the second pilot code signal, the centroid tracking circuit comprising:

an analog-to-digital converter, responsive to a clock signal and the received CDM, to produce a sequence of sample values including a set of even numbered sample values and a set of odd-numbered sample values;

wherein the even numbered samples and the odd-numbered samples are interleaved in time and the 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;

means for combining each of said plurality of phase-delayed versions of the second pilot code signal 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, wherein each of said plurality of phase-delayed versions of the second pilot code signal has a respective a code phase and code symbol period, and each being a code phase-shifted version of a code sequence corresponding to the second pilot code signal;

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; and

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

14. The CDMA modem as recited in claim 13, wherein the means for processing the plurality of early despread multipath signals and for processing the plurality of late despread multipath signals comprises:

a first plurality of accumulators which accumulate the 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.

15. The CDMA modem as recited in claim 14, 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 odd and even signal samples to the respective first and second summing networks.