Correlator co-processor for CDMA RAKE receiver operations

Details Correlator co-processor for CDMA RAKE receiver operations Correlator co-processor for CDMA RAKE receiver operations

2000-06-30

2003-11-18

Bocure, Tesfaldet (Department: 2631)

Pulse or digital communications

Spread spectrum

Direct sequence

C370S342000

Reexamination Certificate

active

06650694

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to RAKE receivers, and more particularly to a multiple channel programmable correlator co-processor (CCP) that supports CDMA base-station and handset RAKE receiver operations.
2. Description of the Prior Art
A RAKE receiver is a radio receiver that includes a plurality of independent receiver units, most commonly referred to as RAKE branches, each of which receives and operates as a diversity combiner of multipath propagated signals. RAKE receivers are especially used in CDMA receivers, among others. RAKE receivers generally involve correlations and accumulations associated with a particular wireless communication protocol wherein each RAKE branch is dedicated to processing the multipath propagated signals in a predetermined manner to accommodate a desired communication protocol. U.S. Pat. No. 5,978,423, entitled
Method and Arrangement of Signal Tracking and A Rake
-
Receiver Utilizing the Arrangement
, issued Nov. 2, 1999 to Farjh and U.S. Pat. No. No. 5,917,851, entitled
Method for Allocating Rake Branches and Rake Receiver
, issued Jun. 29, 1999 to Jarvela et al. exemplify prior art RAKE receiver techniques and architectures in which RAKE branches are permanently allocated to fixed signal processing tasks.
In view of the foregoing discussion, a need exists in the wireless communications art for a programmable, highly flexible, vector-based correlation machine capable of performing CDMA base-station and handset RAKE receiver operations such as finger spreading and search, among other things, for multiple channels, regardless of the particular wireless communication protocol.
SUMMARY OF THE INVENTION
The present invention is directed to a Correlator Co-Processor (CCP) particularly suitable for supporting spread-spectrum CDMA communication systems such as IMT2000-DS (3.84 MHz chip rate specification), IMT2000-MC, IMT2000-TDD, and CDMAOne/IS-95 as well as GPS. The CCP is a programmable, highly flexible, vector-based correlation machine that performs CDMA base-station and mobile-station RAKE receiver operations. The CCP is a centralized correlation machine that can be used for various RAKE receiver tasks such as finger spreading and search, among other things, to accommodate most functions common to RAKE receivers, regardless of the particular wireless protocol. Each RAKE receiver task uses a common centralized data path of the CCP in a time-multiplexed fashion, so that many different tasks can be simultaneously performed on the CCP. The main data path is vectorized in order to reduce power dissipation.
Sharing of the CCP main data path for various RAKE receiver functions, e.g. finger demodulation, code tracking loops and search, accommodates a CCP structure that has programmably configurable resources, rather than hardwired resources common to known architectures. The amount of CCP resources is allocated in any desired way to accommodate a given situation. Unused CCP resources are disabled to preserve power dissipation.
The CCP is capable of performing complex valued correlations that consist of de-spreading and coherent accumulation. The CCP is also capable of performing non-coherent accumulations such as accumulating “symbol” energy values and returning the accumulated energy values for a specified window of offsets for search operations. The CCP, for example, can accumulate early, on-time and late samples of a RAKE finger for use in a finger's code-tracking loop (typically a delay-lock loop (DLL)).
One preferred embodiment of the CCP comprises a Data Path having “multipliers” to multiply samples from an input buffer with samples of pseudo noise (PN) and Walsh codes, adder trees to generate partial correlations, a coherent accumulator to sum the current partial correlation with previous partial correlations(s), and a post processing block for performing RMS (sqrt (I
2
+Q
2
)) calculations (sometimes referred to as “energy” values) and non-coherent accumulations. The CCP Data Path preferably employs extensive pipeline stages to maximize computational capacity as well as temporary (“scratch”) memories to store partial correlation and intermediate RMS accumulation results. The preferred embodiment of the CCP further comprises a plurality of output buffers such as a Finger Symbol Buffer, DPE Buffer, LCI Buffer, EOL Buffer, SSC Search Buffer, and/or PSC Search Buffer for supporting various types of tasks and storing task results. According to the preferred embodiment, the CCP further comprises PN and Walsh generators, a Controller, a Task Buffer, an Interrupt Generator and Configuration Parameter storage units.
The present invention thus provides various technical advantages. In one aspect of the invention, a programmable, highly flexible, vector-based correlator co-processor is provided to support a plurality of CDMA base-station and mobile-station RAKE receiver operations.
In another aspect of the invention, a centralized correlation machine is provided to accomplish various RAKE receiver tasks such as finger de-spreading and search.
In yet another aspect of the invention, a correlator co-processor is provided with a centralized data path capable of supporting time-multiplexed operations such that many different tasks can be simultaneously performed by the correlator co-processor.
In still another aspect of the invention, a correlator co-processor for supporting a plurality of CDMA base-station and mobile-station RAKE receiver operations is provided with a vectorized main data path to reduce power dissipation.
According to another aspect of the invention, a correlator co-processor having a shared data path is programmably configurable to accommodate a plurality of CDMA base-station and mobile-station RAKE receiver operations without necessitating “hardwired” structural elements.
According to yet another aspect of the invention, a correlator co-processor for supporting a plurality of CDMA base-station and mobile-station RAKE receiver operations is capable of performing complex valued correlations consisting of de-spreading and coherent accumulation and is further capable of accumulating “symbol” energy values (non-coherent accumulations).
In still another aspect of the invention, a correlator co-processor for supporting a plurality of CDMA base-station and mobile-station RAKE receiver operations is configurable to support the IMT2000-DS (3.84 MHz chip rate specification), IMT2000-MC, IMT2000-TDD, CDMAOne/IS-95 and GPS wireless protocols.
As used herein, the following terms have the following meanings.
“3G” means 3
rd
generation.
“ABB” means analog baseband (cf AFE).
“A/D (ADC)” means analog to digital converter.
“AFC” means automatic frequency control.
“AFE” means analog front end (cf ABB).
“AGC” means automatic gain control.
“ARIB” means Association of Radio Industries and Businesses (Japan).
“ARM” means advance RISC machine.
“BS” means base station.
“CCP” means correlator co-processor.
“CDMA” means code division multiple access.
“CPICH” means common pilot channel.
“D/A (DAC)” means digital to analog converter.
“DBB” means digital baseband.
“DLL” means delay lock loop.
“DMA” means direct memory access.
“DPCCH” means dedicated physical control channel.
“DPE (DPPE)” means delay profile estimation.
“DPP” means delay path power.
“DSP” means digital signal processor/processing.
“DSPRDC” means DSP Research and Development Center.
“ETSI” means European Telecommunications Standards Institute.
“FSC” means first short code.
“GPS” means global positioning system.
“HW” means hardware.
“ITU” means International Telecommunications Union.
“L1” means layer
1
(physical layer).
“L2” means layer
2
(link layer).
“L3” means layer
3
(network layer).
“LC” means long code.
“LCI” means long code indicator.
“LFSR” means linear feedback shifter register.
“MS” means mobile station.
“PICH” means paging indication channel.
“PN” means pseudo noise.
“PSC” means primary search code.
“RF” means radio frequency.
“RTT” means radio transmission technology.
“RX” means receive/receiver.
“SC” means short code.
“S

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