Sub-symbol matched filter-based frequency error processing for spread spectrum communication systems

• US 6,366,626 B1
• Filed: 09/23/1998
• Issued: 04/02/2002
• Est. Priority Date: 09/26/1997
• Status: Expired due to Term

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Wherenet Corporation (Zebra Technologies Corporation)
• Inventors: Boyd, Robert W.
• Primary Examiner(s): Ghayour, Mohammad H.
• Application Number:
  US09/159,242
• Time in Patent Office: 1,287 Days
• Field of Search: 375/343, 375/350, 375/142, 375/143, 375/150, 375/152, 333/165, 342/189, 327/317, 327/319
• US Class Current: 375/343
• CPC Class Codes: H03H 17/0254 Matched filters
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 2201/70711 with modular structure

Abstract

To accommodate the large frequency uncertainty associated with low cost spread spectrum systems, a matched filter architecture is subdivided into cascaded sub-symbol filter segments, the number of which is selected to prevent loss of unacceptable signal energy over the received signal frequency uncertainty. The sub-symbol filter segments are processed in plural phase rotation-signal combiner stages, outputs of which are associated with multiple frequency bins. A respective phase rotation-signal combiner stage multiplies sub-symbol filter segments by respectively offset phase rotation vectors, associated with the plural frequency bins. The sub-symbol phase vector products of each stage are summed to produce plural frequency bin outputs.

Claims

1. A matched filter of temporal length T_s for processing a broadband signal of frequency uncertainty δ

_f comprising;

a plurality of N cascaded sub-symbol matched filter segments, each of which has a duration T_s/N sufficient to prevent loss of signal energy over said frequency uncertainty δ

_f that would prevent recovery of said broadband signal;

a plurality of K phase rotation-signal combiner stages, outputs of which are associated with K frequency bins of said matched filter, a respective phase rotation-signal combiner stage being operative to produce a summation of products of outputs of said sub-symbol filter segments and a respective set of mutually offset phase rotation vectors.

2. A matched filter according to claim 1, wherein said respective set of mutually offset phase rotation vectors comprises integral multiples of a prescribed phase vector value.

3. A matched filter according to claim 2, wherein said prescribed phase vector value comprises an integral multiple of π

/2.

4. A matched filter according to claim 1, wherein said broadband signal comprises a spread spectrum signal.

5. A matched filter according to claim 1, wherein a respective phase rotation-signal combiner stage comprises a plurality of N multipliers that are operative to multiply the outputs of said N sub-symbol filter segments by a set of K mutually differentially offset phase rotation vectors, and an adder which sums N sub-symbol phase vector products of a respective one of said K phase rotation-signal combiner stages to produce a respective one of the K frequency bin associated outputs.

6. A matched filter according to claim 5, wherein a set of mutually differentially offset phase rotation vectors comprises integral multiples of a prescribed phase vector value.

7. A matched filter according to claim 6, wherein said prescribed phase vector value comprises an integral multiple of π

/2.

8. A matched filter according to claim 1, wherein a respective phase rotation-signal combiner stage comprises an adder and direct and inverted connections between said sub-symbol segments and said adder.

9. A matched filter according to claim 8, wherein a set of mutually differentially offset phase rotation vectors comprises integral multiples of a prescribed phase vector value.

10. A matched filter according to claim 9, wherein said prescribed phase vector value comprises an integral multiple of π

/2.

11. A method for processing a broadband signal of frequency uncertainty δ

_f comprising the steps of;

(a) coupling said broadband signal through successive ones of a plurality of N cascaded sub-symbol matched filter segments of a matched filter of temporal length T_s, each sub-symbol matched filter segment having a duration T_s/N sufficient to prevent loss of signal energy over said frequency uncertainty δ

_f that would prevent recovery of said broadband signal;

(b) generating K summations of products of said N sub-symbol filter segments and K respectively different sets of N mutually offset phase rotation vectors, said K summations being associated with K respectively different frequency bins; and

(c) selecting the largest of said K summations generated in step (b).

12. A method according to claim 11, wherein a respective set of mutually offset phase rotation vectors comprises integral multiples of a prescribed phase vector value.

13. A method according to claim 12, wherein said prescribed phase vector value comprises an integral multiple of π

/2.

14. A method according to claim 11, wherein step (b) comprises multiplying outputs of said N sub-symbol filter segments by respectively different sets of K mutually differentially offset phase rotation vectors, and summing resulting N sub-symbol phase vector products to produce K frequency bin associated signal outputs.

15. A method according to claim 11, wherein step (b) comprises providing direct and inverted connections between said sub-symbol segments and K respective adders.

16. A method according to claim 11, wherein said broadband signal comprises a spread spectrum signal.