Multipath resistant, orthogonal code-division multiple access system

• US 5,987,014 A
• Filed: 07/14/1994
• Issued: 11/16/1999
• Est. Priority Date: 07/14/1994
• Status: Expired due to Term

• Current Assignee: Alcatel USA Sourcing L.P. (Nokia Corporation)
• Original Assignee: Stanford Telecommunications, Inc. (Nokia Corporation)
• Inventors: Chen, Horen, Magill, David T.
• Primary Examiner(s): NGUYEN, CHAU T
• Application Number:
  US08/274,556
• Time in Patent Office: 1,951 Days
• Field of Search: 370/18, 370/19, 370/21, 370/22, 370/335, 370/342, 370/209, 375/200, 375/205, 375/206, 375/40, 375/96, 375/100, 375/208, 375/367, 455/52.1, 455/65
• US Class Current: 370/335
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 2001/70706 using a code tracking loop, e.g. a delay locked loop
• CPC Class Codes: H04J 13/004 Orthogonal
• CPC Class Codes: H04J 13/12 Generation of orthogonal codes

Abstract

The present invention is directed to the use of bandwidth efficient OCDMA in a multipath environment. The high rate PN code greatly attenuates multipath components that are delayed enough to have significant impact on the degree of orthogonality that may be achieved. By offsetting the carriers by the RW chipping rate and using precise network timing to align all accesses to a small fraction of a high rate PN chip duration, it is possible to fully utilize the available bandwidth. The procedure for achieving this time base alignment has been previously disclosed in U.S. patent application Ser. No. 980,957.

Claims

1. In an orthogonal code division multiple access (OCDMA) wireless telephone system having a base station and a plurality of mobile transceiver handsets, sending modulator and receiving demodulator means in said base station and each said mobile transceiver handset, respectively, the improvement for making said OCDMA system more tolerant of multipath delay spread, comprising, each said sending modulator means having 8 to 64 PN chips per each Rademacher-Walsh (RW) chip, each receiving demodulator means having a correlator for providing a demodulator output signal;

and each modulator means including means for setting the PN chipping rate high enough such that said correlators provide processing gain discrimination against multipath signal components delayed more than a small fraction of a RW chip duration.

2. A process for making an orthogonal code division multiple access (OCDMA) wireless telephone system more tolerant of multipath delay, said OCDMA wireless telephone system having a base station and a plurality of mobile transceiver handsets, modulator and demodulator means in said base station and each said mobile transceiver handset comprising, causing said modulator to have between 8 to 64 PN chips per each Rademacher-Walsh (RW) chip, each demodulator having a correlator for providing a demodulator output signal;

the steps of setting the PN chipping rate at a level at each (1) modulator and (2) demodulator such that said correlators provide processing gain discrimination against multipath signal components delayed more than a small fraction of a RW chip duration.

3. In an orthogonal code division multiple access (OCDMA) radio communication system in which a set of orthogonal Rademacher-Walsh (RW) functions are overlaid with a pseudo-noise (PN) sequence forming a coded spreading sequence for an information signal, each orthogonal function of said set carrying voice/data for a single user in said system and a source of selected carrier signals and means to modulate the information signals onto a selected carrier signal to form a transmit signal, said system having a base station and a plurality of mobile transceiver handsets, sending modulator and receiving demodulator means in said base station and each said mobile transceiver handset, respectively, the improvement comprising each said sending modulator means having PN chips in the range of eight to sixty-four PN chips per each RW chip, each receiving demodulator means having a correlator for providing a demodulator output signal and each modulator means including means for setting the PN chipping rate high enough such that the correlator provides processing gain discrimination against multipath signal components delayed more than a small fraction of an RW chip duration.

4. In an orthogonal code division multiple access (OCDMA) radio communication system in which a set of orthogonal Rademacher-Walsh (RW) functions are overlaid with a pseudo-noise (PN) sequence forming a coded spreading sequence for an information signal, each orthogonal function of said set carrying voice/data for a single user in said system and a source of selected carrier signals and means to modulate the information signals onto a selected carrier signal to form a transmit signal, said system having a base station and a plurality of mobile transceiver handsets, sending modulator and receiving demodulator means in said base station and each said mobile transceiver handset, respectively, the improvement comprising each said sending modulator means having PN chips in the range of eight to sixty-four PN chips per each RW chip, each receiving demodulator means having a correlator for providing a demodulator output signal and each modulator means including means for setting the PN chipping rate high enough such that the correlator provides processing gain discrimination against multipath signal components delayed more than a small fraction of an RW chip duration wherein said communications system includes an orthogonal frequency-division multiple access system in which the transmitted signal is given by:

space="preserve" listing-type="equation">S.sub.ik (t)=PN.sub.HR (t)·

PN.sub.LR (t)·

RW.sub.i (t) ·

{α

(t)+jb(t)}·

cos (ω

.sub.o t+δ

ω

·

k·

t)

where PN_HR (t) is the high rate PN code for a set of accesses, PN_LR (t) is the low rate PN code for set of accesses, RW_i (t) is i-th RW function, |α

(t)+jb(t)| is the complex-valued baseband data modulated signal; and

book is the amount of angular frequency offsetting which corresponds to 2π

times integer multiples of the RW chipping rate.