Apparatus and method for parallel searching and correlating for CDMA system

• US 6,519,237 B1
• Filed: 05/28/1999
• Issued: 02/11/2003
• Est. Priority Date: 05/28/1999
• Status: Expired due to Fees

• Current Assignee: Breakwaters Innovations LLC
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: McDonough, John, Iraninejad, Mehraban
• Primary Examiner(s): Bost, Dwayne
• Assistant Examiner(s): Old, Gregory V.
• Application Number:
  US09/321,680
• Time in Patent Office: 1,355 Days
• Field of Search: 370/335, 370/342, 370/350, 375/130, 375/140, 375/142, 375/147, 375/150, 375/149
• US Class Current: 370/335
• CPC Class Codes: H04B 1/708 Parallel implementation
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception

Abstract

A method to expediently perform search/correlation operation between an internal pilot pseudonoise (PN) sequence and an incoming pilot PN sequence. This operation is used to acquire base stations in a Code Division Multiple Access (CDMA) system. In one embodiment, the present invention recites a method comprising several steps. First, a plurality of PN sequence values are provided internally and an input signal sample is received. The input signal sample is correlated, in parallel, with the plurality of PN sequence values. The correlation operation is performed at a rate equivalent to the input sample rate times the number of PN sequence values being correlated in parallel, assuming a resolution of one. The resultant products are respectively summed and stored in a plurality of accumulators.

Claims

1. In a communication system, a method of expediently correlating a pilot pseudonoise (PN) sequence with an incoming signal, said method comprising the steps of:

a) providing a plurality of sequential PN sequence values forming an initial set of PN sequence values wherein said plurality of PN values forms an S bit array of PN sequence values;

b) receiving an input signal sample;

c) despreading said input signal sample with each of said plurality of sequential PN sequence values to obtain a plurality of products;

d) adding each of said products to a stored value in a respective one of a plurality of product accumulators to obtain a plurality of sums;

e) writing each of said sums back to said respective one of said plurality of product accumulators;

f) receiving a new PN sequence value;

g) indexing said S bit array to accommodate said new PN sequence value such that a new S bit array is formed having a plurality of PN sequence values;

h) repeating steps b) through e) for said new S bit array;

i) repeating steps f) through h) for N cycles;

j) dumping said stored value from each of said plurality of first accumulators after said N cycles have occurred and resetting said stored value for each of said plurality of first accumulators; and

k) calculating an energy value for said stored value dumped from each of said plurality of first accumulators wherein S and N are positive integers.

2. The method recited in claim 1 wherein said input signal sample occurs as a result of sampling at a first rate, and steps c) through e) are performed at a clock rate equivalent to said first rate times the quantity sequence values used in said initial set of PN sequence values.

3. The method recited in claim 1 further comprising the steps of:

l) adding said total energy with a stored energy value from a respective one of a plurality of energy accumulators to obtain an energy sum;

m) writing said energy sum into said respective one of said plurality of energy accumulators;

n) repeating steps f) through m) for M cycles where M is a positive integer;

o) dumping said stored energy value from each of said plurality of energy accumulators to a controller and resetting said stored energy value to zero for each of said plurality of energy accumulators;

p) providing a new initial set of PN sequence values, said new initial set of PN sequence values incremented, away from said initial set of PN sequence of values used in step a), by said quantity of PN sequence values used in step a); and

q) repeating steps b) through p) until phase shifts through the PN sequence have been accounted for.

4. The method recited in claim 3 wherein steps a) through p) are performed for each of a plurality of search engines, coupled to each other, as determined by the desired precision of said search operation.

5. A searcher providing an expedient search operation, said searcher comprising:

an input lead for an in-phase signal;

an input lead for a quadrature-phase signal;

at least one quadrature despreader (QDS) coupled to said input lead for said in-phase signal and to said input lead for said quadrature-phase signal;

at least one product accumulator (PA), said product accumulator coupled to said at least one QDS;

at least one squaring circuit (SC), said at least one SC coupled to said at least one PA;

at least one energy accumulator (EA), said at least one EA coupled to said at least one SC;

an output lead;

and a PN input lead; and

a controller, said controller coupled to said at least one QDS, to said at least one PA, to said at least one SC, and to said PN input lead, and to said at least one EA said controller containing program instructions to execute a method for performing a parallel search/correlation operation, said method comprising the steps of;

a) despreading an input signal sample with each of a plurality of PN sequence values to obtain a plurality of products, said multiplication step performed within the period of an input signal sample, thus effectively performing a parallel search over multiple phase shifts;

b) accumulating each of said plurality of products separately;

c) indexing said plurality of PN sequence values to yield a new plurality of PN sequence values;

d) repeating steps a) and b) with said new plurality of PN sequence values, for N cycles;

e) determining an energy for each of said plurality of products;

f) repeating steps a) through e) for M cycles where M and N are positive integers;

g) providing a new initial set of PN sequence values, said new initial set of PN sequence values incremented, away from said initial set of PN sequence values used in step a), by said quantity of PN sequence values used in step a); and

h) repeating steps b) through g) until phase shifts through the entire PN sequence have been accommodated for.