Blind Estimation of Direct Sequence Spread Spectrum Signals(4)

Abstract—Self-recovering receivers for direct-sequence spreadspectrum signals with unknown spreading codes are discussed in this paper. Applications include signal interception, jamming, and low probability of intercept (LPI) communications. A multirate/m

1244IEEE TRANSACTIONS ON SIGNAL PROCESSING,VOL.45,NO.5,MAY1997 advantage is that it does not require the

input

,have no

common roots.

ii)for at least

one

for at least

one

Of the above three conditions,only i)is indeed restrictive;

ii)and iii)are always satisfied,provided that the vector

channel

order

has

no

Proposition2is easier to interpret in the context of DS/SS

systems.The identifiability requirement amounts to not

having

,

i.e.,

,equispaced on a circle.

The

sequence has

only zeros,and they are

typically not distributed around a circle(or can be designed

that way).Moreover,since,typically,the order

of is such

that has less

than

,and the condition is

valid for any

code of

length

.Then,using

(12),can be written

as

(16)

where

rows.

Finally,

.From(16),the data correlation

matrix

(provided that the number of

columns is less than the number of

rows is also

full rank,then

range.

Let us define the noise subspace

of

be the matrix

containing those eigenvectors.

Then,

(21)

where

and

(22)

The

matrix

is

.

Some remarks on the application of this method to the

DS/SS setup are now in order:

1)The subspace identification method requires an SVD to

be performed on

a

can be fairly small

since

,

and

,the

order increases only

to

(and,hence,the number of equivalent FIR

channels)is large,typically in the order of hundreds

of chips.To ease the computational burden and memory

requirements,one could divide the problem into two(or

more)

with(or a fraction