Increased capacity in an OCDMA system for frequency isolation

• US 6,317,412 B1
• Filed: 12/12/1997
• Issued: 11/13/2001
• Est. Priority Date: 12/12/1997
• Status: Expired due to Term

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Stanford Telecommunications, Inc. (Nokia Corporation)
• Inventors: Ohlson, John, Natali, Francis D.
• Primary Examiner(s): NGO, RICKY QUOC
• Application Number:
  US08/989,466
• Time in Patent Office: 1,432 Days
• Field of Search: 370/208, 370/209, 370/328, 370/329, 370/330, 370/335, 370/341, 370/342, 370/441, 370/478, 370/479, 455/446, 455/447, 455/450, 455/454
• US Class Current: 370/208
• 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]

Abstract

A spread spectrum OCDMA communication system in which multiple base stations or beams from a satellite are deployed in a “cellular” coverage structure, system capacity is increased by dividing the available spectrum into non-overlapping frequency segments which are assigned to different cells in a frequency reuse pattern to provide greater system capacity than full frequency reuse in each cell.

Claims

1. In a spread spectrum CDMA communication system in which a base station communicates with a multiplicity of subscriber terminals and the signal transmitted by the base station is comprised of a set of substantially 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 of substantially orthogonal functions carries data for a single user in said system, a source of selected carrier signals and a modulator to modulate said information signal onto a carrier to form a transmit signal and said coded spreading sequence on said transmit signal for broadcasting, each subscriber terminal has a receiver with a demodulator for coherently demodulating a base station signal and multiple base stations are deployed in a “

cellular”

coverage structure, the improvement comprising increasing system capacity by dividing an available spectrum into non-overlapping frequency segments which are assigned to different cells in a frequency reuse pattern to provide greater system capacity than full frequency reuse in each cell.

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

3. The system of claim 1 which further comprises at least one repeater for receiving the base station signal and translating the signal to a form suitable for an intended recipient user.

4. The OCDMA system of claim 1 in which each base station receives a plurality of spread spectrum signals from a corresponding plurality of subscriber stations on a frequency channel, each signal from a subscriber station being composed of data symbols overlaid with one set of orthogonal functions and a pseudo-noise sequence, said signals from subscriber stations being synchronized to arrive at said base station in time and frequency.

5. In a spread spectrum CDMA communication method in which one or more base stations communicate with a multiplicity of subscriber terminals located in different beams of a multi-beam satellite relay system, said base station(s) transmits a signal for each beam which is comprised of a set of substantially 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 of substantially orthogonal functions carries data for a single user in said beam, a source of selected carrier signals and a modulator to modulate said information signal onto a carrier to form a transmit signal and said coded spreading sequence on said transmit signal for broadcasting, each subscriber terminal has a receiver with a demodulator for coherently demodulating the base station signal, the improvement comprising:

the steps of dividing an available spectrum into non-overlapping frequency segments and assigning to different cells in a frequency reuse pattern to provide greater system capacity than full frequency reuse in each beam.

6. The system of claim 5 in which the data intended for each user is voice data.

7. The OCDMA system of claim 5 in which each base station receives a plurality of spread spectrum signals from a corresponding plurality of subscriber stations on a frequency channel, each signal from a subscriber station being composed of data symbols overlaid with one set of orthogonal functions and a pseudo-noise sequence which is time shifted or different for adjacent beams, and synchronizing said signals from subscriber stations to arrive at said base station in time and frequency synchronism.