Flux density reduction in OCDMA satellite communication system

• US 6,075,781 A
• Filed: 05/19/1998
• Issued: 06/13/2000
• Est. Priority Date: 12/12/1997
• Status: Expired due to Term

• Current Assignee: Alcatel USA Sourcing L.P. (Nokia Corporation)
• Original Assignee: Stanford Telecommunications, Inc. (Nokia Corporation)
• Inventors: Natali, Francis D., Ohlson, John
• Primary Examiner(s): Kizou, Hassan
• Assistant Examiner(s): HO, DUC CHI
• Application Number:
  US09/080,952
• Time in Patent Office: 756 Days
• Field of Search: 370/203, 370/208, 370/206, 370/209, 370/210, 370/320, 370/342, 370/485, 455/13-4
• US Class Current: 370/342
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A spread spectrum CDMA communication system in which base stations communicate with a plurality of subscriber terminals located in different beams of a multi-beam satellite relay system. A base station transmits a signal for each beam which is comprised of a set of orthogonally spaced subcarriers, each of which is modulated by a set of orthogonal functions which are overlaid with a pseudo-noise (PN) sequence forming a coded spreading sequence for an information signal. Each orthogonal function carries data for a single user in the beam. Selected carrier signals are modulated with information signals onto the subcarriers to form a beam signal. The available frequency spectrum is divided into non-overlapping segments which are assigned to different beams in a 1:N_ru frequency reuse pattern. Each subscriber terminal has a receiver which coherently demodulate the base station signal. A PN spreading code, P2, with chipping rate N_ru χR_c is applied to all of the beam signals simultaneously to spread the signal energy over a wider bandwidth to reduce the power spectral density in each beam. The receiver correlates the received signal with a synchronized replica of P2 to remove P2 from the incoming signal without affecting beam-to-beam frequency isolation. The subcarriers of the beam signal are orthogonally spaced across the available frequency spectrum with spacing N_ru χR_c and N_ru distinct sets of subcarriers frequencies are formed to be assigned in the 1:N_ru beam frequency reuse pattern.

Claims

1. A spread spectrum CDMA communication system in which one or more receiver equipped base stations communicate with a multiplicity of receiver equipped subscriber terminals located in different beams of a multi-beam satellite relay system, the base station(s) transmits a signal for each beam which is comprised of a set of orthogonally spaced subcarriers, each of which is modulated by a set of orthogonal, or nearly orthogonal, functions which are overlaid with a pseudo-noise (PN) sequence forming a coded spreading sequence for an information signal, each orthogonal function of said set carriers data for a single user in said bean, a source of selected carrier signals and means to modulate said information signals onto said subcarriers to form a beam signal and said coded spreading sequence on said beam signal, and wherein the available frequency spectrum is divided into nonoverlapping or orthogonal frequency segments which are assigned to different beams in a 1:

N_ru frequency reuse pattern and each subscriber terminal has a receiver with means to coherently demodulate the base station signal, the improvement comprising;

a circuit at said base station for applying a PN spreading code, P2, with chipping rate N_ru χ

R_c to all of the beam signals simultaneously to spread the signal energy over a wider bandwidth in order to reduce the power spectral density in each beam, and

a circuit in the receiver for correlating a received signal with a synchronized replica of P2 to remove P2 from the incoming signal without affecting beam-to-beam frequency isolation.

2. The system of claim 1 in which the subcarriers of the beam signal are orthogonally spaced across the available frequency spectrum with spacing N_ru χ

R_c and N_ru distinct sets of subcarrier frequencies are formed to be assigned in the 1;

N_ru beam frequency reuse pattern.

3. The system of claim 1 in which the data intended for each user is voice data.

4. In a spread spectrum CDMA satellite communication system, in which more than one satellite illuminates the same region on the earth, and one or more receiver equipped base stations communicate with a multiplicity of receiver equipped subscriber terminals located in different beams of the multi-beam satellite relay system, and the base station(s) transmits a signal for each beam which is comprised of a set of orthogonally spaced subcarriers, each of which is modulated by a set of orthogonal, or nearly orthogonal, functions which are overlaid with a pseudo-noise (PN) sequence forming a coded spreading sequence for an information signal, each orthogonal function of said set carries data for a single user in said beam, a source of selected carrier signals and means to modulate said information signals onto said subcarriers to form a beam signal and said coded spreading sequence on said beam signal, and wherein the available frequency spectrum is divided into non-overlapping or orthogonal frequency segments which are assigned to different beams in a 1:

N_ru frequency reuse pattern and each subscriber terminal has a receiver with means to coherently demodulate the base station signal, the improvement comprising;

a circuit at said base station for applying a PN spreading code, P3, with a chipping rate N_ru χ

R_c simultaneously to spread the signal energy over a wider bandwidth in order to reduce the power spectral density in each beam and reduce interference from neighboring satellites, and

a circuit in the receiver for correlating a received signal with a synchronized replica of P2 to remove P2 from the incoming signal without affecting beam-to-beam frequency isolation.

5. The system of claim 4 in which the subcarriers of the beam signal are orthogonally spaced across the available frequency spectrum with spacing N_ru χ

R_c and N_ru distinct sets of subcarrier frequencies are formed to be assigned in the 1;

N_ru beam frequency reuse pattern.

6. The system of claim 4 in which the data intended for each user is voice data.

7. A spread spectrum CDMA satellite communication system, in which another satellite communication system illuminates the same region on the earth, and one or more receiver equipped base stations communicate with a multiplicity of receiver equipped subscriber terminals located in different beams of the multi-beam satellite relay system, and the base station(s) transmits a signal for each beam which is comprised of a set of orthogonally spaced subcarriers, each of which is modulated by a set of orthogonal, or nearly orthogonal, functions which are overlaid with a pseudo-noise (PN) sequence forming a coded spreading sequence for an information signal, each orthogonal function of said set carries data for a single user in said beam, a source of selected carrier signals and means to modulate said information signals onto said subcarriers to form a beam signal and said coded spreading sequence on said beam signal, and wherein the available frequency spectrum is divided into non-overlapping or orthogonal frequency segments which are assignee to different beams in a 1:

N_ru frequency reuse pattern, and each subscriber terminal has a receiver with means to coherently demodulate the base station signal, the improvement comprising;

a circuit at said base station for applying a PN spreading code, P2, with chipping rate N_ru χ

R_c to all of the beam signals simultaneously to spread the signal energy over a wider bandwidth in order to reduce the power spectral density in each beam,

a circuit in the receiver for correlating a received signal with a synchronized replica of P2 to remove P2 from the incoming signal without affecting beam-to-beam frequency isolation.

8. The system of claim 7 in which the subcarriers of the beam signal are orthogonally spaced across the available frequency spectrum with spacing N_ru χ

R_c and N_ru distinct sets of subcarrier frequencies are formed to be assigned in the 1;

N_ru beam frequency reuse pattern.

9. The system of claim 7 in which the data intended for each user is voice data.

10. In a spread spectrum CDMA satellite communication system, in which another satellite communication system illuminates the same region on the earth, and a multiplicity of receiver equipped subscriber terminals located in different beams of the multi-beam satellite relay system communicate with one or more receiver equipped base stations, and the subscriber terminals transmit a signal which is comprised of one of a set of orthogonally spaced subcarriers, which is modulated by one of a set of orthogonal, or nearly orthogonal, functions which are overlaid with a pseudo-noise (PN) sequence forming a coded spreading sequence for an information signal, the orthogonal function of said set carries data for transmission to the base station in said beam, a source of the selected subcarrier signal and means to modulate said information signal onto said subcarrier to form a return link signal and said coded spreading sequence on said return link signal, wherein the available frequency spectrum is divided into non-overlapping or orthogonal frequency segments which are assigned to different beams in a 1:

N_ru frequency reuse pattern, each base station has a receiver(s) with means to coherently demodulate the subscriber terminal signal, the improvement comprising;

a PN spreading code, P2, with chipping rate N_ru χ

R_c is applied to the subscriber terminal transmit signal to spread the signal energy over a wider bandwidth in order to reduce the transmit power spectral density, and

a circuit in the base station receiver for correlating a received signal with a synchronized replica of P4 to remove P2 from the incoming signal without affecting beam-to-beam frequency isolation.

11. The system of claim 10 in which the subcarriers in a beam are orthogonally spaced across the available frequency spectrum with spacing N_ru χ

R_c and N_ru distinct sets of subcarrier frequencies are formed to be assigned in the 1;

N_ru beam frequency reuse pattern.

12. The system of claim 10 in which the data intended for each user is voice data.