Multi-user communication system architecture with distributed receivers

• US 5,608,722 A
• Filed: 04/03/1995
• Issued: 03/04/1997
• Est. Priority Date: 04/03/1995
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Miller, David S.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Nguyen, Chau T.
• Application Number:
  US08/415,958
• Time in Patent Office: 701 Days
• Field of Search: 370/18, 370/19, 370/20, 370/22, 370/100.1, 370/95.1, 375/267, 375/259, 375/200, 375/206, 375/210, 375/373, 375/371, 375/205
• US Class Current: 370/320
• CPC Class Codes: H04B 7/0845 per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch rake receivers as such H04B1/7115
• CPC Class Codes: H04B 7/0891 Space-time diversity rake receivers H04B1/7115; space-time decoding H04L1/0631
• CPC Class Codes: H04B 7/18513 Transmission in a satellite or space-based system
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]
• CPC Class Codes: H04B 7/2628 using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] H04B7/2618 takes precedence

Abstract

Method and apparatus for receiving signals in gateways for satellite repeater type spread spectrum communication systems making more efficient use of data transfer capacity and diversity processing. Several communication signals are received by multiple analog receivers and converted into digital format. The digital communication signals are transferred from each analog receiver into a series of demodulation or FHT modules in which they are first despread into encoded data symbols using predetermined PN coding sequences, and then mapped into symbol energy metrics using orthogonal transformers, such as fast Hadamard transformers. The transformation output for each communication channel from each analog receiver is input to a single metric receiver for a data channel or subscriber, where it is subjected to conventional metric signal processing to reconstruct the data. A set of dedicated modules is coupled to each analog receiver for handling each diversity path or subscriber active communication system channel being transferred through that receiver or analog path. Each demodulation or FHT module comprises despreading elements and FHT components that are easily distributed in processing arrays within the gateway.

Claims

1. A method for receiving signals in a spread spectrum communication system in which information is communicated by orthogonally encoded channels within communication signals, comprising the steps of:

receiving communication signals over one or more diversity transfer paths from one or more system subscribers using one or more analog receivers, and converting them to digital communication signals;

applying said digital communication signals to a corresponding set of demodulating modules connected to each analog receiver, the number of modules being equal to the product of a predetermined maximum number of subscribers to be serviced by a receiver and a maximum expected average number of signal paths over which communication signals are to be received from each subscriber;

despreading each of said digital communication signals using preselected pseudorandom noise (PN) type code sequences in one portion of said demodulating modules;

transforming at least a preselected number of despread digital communication signals each into energy metric signals indicative of energy values associated with encoded data in another portion of said demodulating modules; and

transferring resulting energy metric signals corresponding to signals intended for a subscriber as an input to at least one metric receiver pre-assigned to said subscriber from a plurality of metric receivers.

2. The method of claim 1 wherein said despreading step generates despread digital communication signals in the form of encoded data symbols and said transforming step comprises the step of transferring encoded data symbols for each signal path to one of a plurality of orthogonal function transformers each for generating symbol energy metrics for a channel operating through a corresponding analog receiver.

3. The method of claim 2 further comprising the step of summing symbol energy metrics received at inputs of each of said metric receivers from multiple transformation steps to generate a single channel symbol energy metric for deriving channel data.

4. The method of claim 2 wherein said orthogonal function transformers comprise Fast Hadamard Transformers.

5. The method of claim 1 wherein each of said metric receivers corresponds to a single encoded signal channel to be processed.

6. The method of claim 1 wherein said analog receivers are configured to receive signals of at least one carrier frequency and convert said signals to digital communication signals at predetermined sampling rates.

7. The method of claim 1 wherein said analog receivers are provided within a gateway type base station and at least one satellite based repeater is employed to transfer said communication signals from subscriber units within said communication system to said analog receivers.

8. The method of claim 7 wherein there are at least two satellites in communication with said gateway at any given time.

9. The method of claim 1 wherein said preselected pseudonoise (PN) sequences are also used to modulate in-phase and quadrature components of digital data signals prior to transmission to intended recipients.

10. The method of claim 9 further comprising the steps of tracking a relative time difference between received communication signals and a phase of said PN sequences being used in despreading, and providing a timing adjustment signal to indicate sign and magnitudes of any difference.

11. Apparatus for receiving signals in a spread spectrum communication system in which information is communicated over orthogonally encoded communication channels within spread spectrum communication signals transmitted by system subscribers, comprising:

one or more analog receivers connected to receive spread spectrum communication signals, each receiver configured to receive signals of at least one carrier frequency and convert said signals to digital communication signals, which are provided at outputs;

a plurality of demodulating means connected to the outputs of each of said analog receivers for despreading each of said digital communication signals using preselected pseudorandom noise (PN) type code sequences to produce encoded data symbols, and for transforming at least a preselected number of said encoded data symbols into energy metric signals indicative of energy values associated with encoded data symbols, said demodulating means configured to accommodate a number of signals equal to the product of a predetermined maximum number of subscribers to be serviced by a receiver and a maximum expected average number of signal paths over which communication signals are to be received from each subscriber through that corresponding analog receiver; and

one or more metric data receivers, each connected to receive energy metric signals from one or more of said demodulating means associated with each analog receiver which are providing metric signals for a pre-assigned single encoded communication channel.

12. The apparatus of claim 11 wherein said demodulating means comprises demodulating modules, the number of modules being equal to the product of a predetermined maximum number of subscribers to be serviced by a receiver and a maximum expected average number of signal paths so that at least one module is available for each diversity communication path over which communication signals are to be received from each subscriber through that corresponding analog receiver, which each comprise:

despreading means for generating despread digital communication signals in the form of encoded data symbols; and

transformation means for receiving said encoded data symbols and for performing orthogonal function transformations to generate symbol energy metrics for a channel operating through a corresponding analog receiver.

13. The apparatus of claim 12 further comprising summation means for summing symbol energy metrics received at inputs of each of said metric receivers from multiple demodulating means to generate a single channel symbol energy metric for deriving channel data.

14. The apparatus of claim 12 wherein said transformation means comprise Fast Hadamard Transformers.

15. The apparatus of claim 11 wherein each of said metric receivers is pre-assigned to a single encoded signal channel to be processed.

16. The apparatus of claim 11 wherein said analog receivers are configured to receive signals of at least one carrier frequency and convert said signals to digital communication signals at predetermined sampling rates.

17. The apparatus of claim 11 wherein said analog receivers are provided within a gateway type base station and at least one satellite based repeater is employed to transfer said communication signals from subscriber units within said communication system to said analog receivers.

18. The apparatus of claim 17 wherein there are at least two satellites in communication with said gateway at any given time.

19. The apparatus of claim 11 wherein said preselected pseudonoise (PN) sequences are also used to modulate in-phase and quadrature components of digital data signals prior to transmission to intended recipients.

20. The apparatus of claim 11 wherein said communication system comprises a wireless telephone/data communication system in which remote users are located within a plurality of cells and communicate information signals to at least one gateway, using code division multiple access (CDMA) spread spectrum type communication signals.