Multiple access communications system and method using code and time division

• US 5,894,473 A
• Filed: 02/29/1996
• Issued: 04/13/1999
• Est. Priority Date: 02/29/1996
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Dent, Paul W.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): HOM, SHICK C
• Application Number:
  US08/608,811
• Time in Patent Office: 1,139 Days
• Field of Search: 370/319, 370/209, 370/329, 370/330, 370/335, 370/337, 370/342, 370/320, 370/441, 375/200, 375/296, 455/63, 455/450, 455/501, 455/436, 455/454, 380/34, 380/37
• US Class Current: 370/342
• CPC Class Codes: H04B 1/56 with provision for simultaneous communication in two directions
• CPC Class Codes: H04B 2201/709727 GRAKE type RAKE receivers
• CPC Class Codes: H04B 7/2618 using hybrid code-time division multiple access [CDMA-TDMA]
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713

Abstract

A multiple access communication system and method using Code Division Multiple Access (CDMA) and Time Division Multiple Access (TDMA) comprises coding information signals with CDMA codewords to be transmitted over a common frequency spectrum, time compressing the CDMA codewords for transmission only during allocated timeslots, activating a receiver only during the allocated timeslots to receive and decompress the time compressed CDMA codewords, and decoding the decompressed CDMA codewords to recover the information signals.

Claims

1. A communication method using Code Division Multiple Access comprising the steps of:

assembling information into blocks of digital data;

coding the blocks of digital data to form spread spectrum codewords;

adding at least two of the spread spectrum codewords to form a composite signal; and

time-compressing the composite signal for transmission in a timeslot.

2. The communication method of claim 1, further comprising the step of scrambling the spread spectrum codewords.

3. The communication method of claim 1, further comprising the step of selectively activating a receiver to receive the time-compressed composite signal during a selected time slot.

4. The communication method of claim 1, further comprising the steps of:

receiving the time-compressed composite signal;

determining a signal strength order corresponding to the spread spectrum codewords contained in the composite signal; and

decoding the spread spectrum codewords in order of greatest to smallest signal strength and subtracting the spread spectrum codewords from the composite signal.

5. A method of communicating using Code Division Multiple Access comprising the steps of:

coding information into digital form to produce a sequence of coded bits;

assembling the coded bits into blocks;

redundantly coding the blocks to form spread spectrum codewords;

scrambling the spread spectrum codewords to form scrambled codewords;

adding at least two of the scrambled codewords to form a composite signal and time compressing the composite signal for transmission in an allocated timeslot.

6. A method of communicating using Code Division Multiple Access comprising the steps of:

coding information using spread spectrum codewords for transmission in an allocated timeslot;

enabling a receiver during the allocated timeslot to receive a composite signal comprising the spread spectrum codewords and an interfering signal;

converting the composite signal into a sequence of numerical samples and storing the numerical samples in a memory;

correlating the numerical samples with one of the spread spectrum codewords at least two points shifted in time to determine numerical values related to a phase and an amplitude of at least two multipath rays;

identifying the spread spectrum codewords using the numerical values to produce a symbol sequence;

reconstructing the information using the symbol sequence.

7. The method of claim 6, wherein said reconstructing step comprises error correction decoding.

8. The method of claim 7, wherein the error correction decoding is carried out with a Reed-Solomon decoder.

9. The method of claim 7, wherein the error correction decoding comprises convolutional decoding.

10. The method of claim 6, wherein the reconstructing step comprises digital voice decoding using at least one of Residual Excited Linear Predictive Coding, Sub-band, and Vector Code Book Excited Linear Predictive Coding speech decoding to produce an analog speech waveform.

11. The method of claim 6, wherein the reconstructing step includes transcoding digitally coded voice from at least one of Adaptive Delta Pulse Code Modulation, Residual Excited Linear Predictive Coding, Sub-band, and Vector Code Book Excited Linear Predictive Coding format to at least one of standard U-Law and A-Law Pulse Code Modulation format for interfacing with a public switched telephone network.

12. A communication apparatus comprising:

block spreading means for assembling digital information into blocks and coding the blocks to produce spread spectrum codewords;

timing means for allocating a timeslot in a repetitive frame period for transmission of the spread spectrum codewords; and

burst formatting means for selecting at least two of the spread spectrum codewords and for time-compressing the at least two of the spread spectrum codewords for transmission in the allocated timeslot.

13. The communication apparatus of claim 12, further comprising scrambling means for combining the spread spectrum codewords with an access code to form scrambled spread spectrum codewords.

14. An apparatus for communicating information signals using Code Division Multiple Access between a fixed station and a mobile station comprising:

spread spectrum coding means for coding the information signals to form spread spectrum codewords;

a transmitter for transmitting a transmitted signal comprising at least two of the spread spectrum codewords during an allocated timeslot;

timing control means for enabling a receiver during the allocated timeslot to receive a composite signal comprising the transmitted signal and interfering signals;

an analog to digital converter for converting the composite signal into a sequence of numerical samples;

a memory for storing the numerical samples;

processing means for recalling the numerical samples from the memory and for processing the numerical samples to establish numerical values related to a phase and an amplitude of at least two rays of the transmitted signal;

a decoder for reproducing the information signals based on the numerical values.

15. The apparatus of claim 14, wherein the spread spectrum coding means is located at the fixed station and the memory is located at the mobile station.

16. The apparatus of claim 14, further comprising source coding means which includes at least one of Adaptive Delta Pulse Code Modulation, Residual Excited Linear Predictive Coding, Sub-band, and Vector Code Book Excited Linear Predictive Coding speech coding means.

17. The apparatus of claim 14, further comprising at least one of convolutional error correction coding means, Reed-Solomon error correction coding means, bit time interleaving means, and symbol time interleaving means.

18. The apparatus of claim 14, wherein the spread spectrum coding means comprises at least one of orthogonal block spreading means, bi-orthogonal block spreading means, and chipwise modulo-2 adding means for scrambling the spread spectrum codewords using an access code.

19. A receiver comprising:

an antenna for receiving a composite signal, the composite signal comprising at least two spread spectrum codewords which are time-compressed into a timeslot;

radio receiver means connected to the antenna for filtering and amplifying the composite signal received by the antenna and for converting the composite signal into complex numerical samples;

timing control means for activating the radio receiver means during the timeslot to thereby reduce power consumption;

a memory for storing the complex numerical samples converted during the timeslot; and

processing means coupled to the memory for processing the stored complex numerical samples, the processing means comprising;

prediction means for predicting a signal strength of each of said spread spectrum codewords and for ordering the spread spectrum codewords in order of strongest to weakest signal strength; and

iterative decoding means for decoding a strongest of the spread spectrum codewords and for subtracting the strongest of the spread spectrum codewords from the composite signal before decoding a next strongest of the spread spectrum codewords.

20. The receiver of claim 19, wherein the processing means comprises a Fast Walsh Transform circuit.

21. The receiver of claim 19, wherein the iterative decoding means subtracts the spread spectrum codewords by setting to zero a transform component computed from the complex numerical samples.

22. The receiver of claim 19, wherein the iterative decoding means subtracts the spread spectrum codewords by despreading the spread spectrum codeword to produce a narrowband signal and removing the narrowband signal with at least one of a notch filter and a bandstop filter.

23. The receiver of claim 19, wherein;

the prediction means predicts the signal strength of individual rays of the composite signal, the rays being received via relatively delayed paths, and orders the rays in order of strongest to weakest signal strength, the signal strength being determined by computing a total energy of the rays of a particular spread spectrum codeword; and

wherein the iterative decoding means subtracts rays of already decoded signals until a predetermined spread spectrum codeword is decoded.

24. A receiver for receiving and decoding information signals comprising:

multiple-element antenna means for receiving and resolving signals from different directions;

multiple-channel processing means, connected to the antenna means, for filtering, amplifying, and digitizing a portion of the received information signals to produce sequences of complex numbers for storage in a memory;

multi-dimensional decimating means for processing the stored sequences of complex numbers to separate the information signals according to channel frequency, time of arrival, and direction of arrival and for producing numerical sequences representative of overlapping Code Division Multiple Access signals;

CDMA signal processing means for processing the numerical sequences to separate individual channel signals transmitted by a single transmitter to produce information symbols; and

source decoding means for processing the information symbols to reconstruct the information signals transmitted by the individual transmitter.

25. The receiver of claim 24, wherein the CDMA signal processing means iteratively decodes the CDMA signals in descending order of received signal strength.

26. The receiver of claim 24, wherein the source decoding means is located at a remote mobile communications gateway exchange and information signals are transmitted to the remote mobile communications gate exchange via a public switched telephone network.

27. A method of communicating using Code Division Multiple Access, comprising the steps of:

forming a narrowband CDMA signal by combining information signals with an access code;

time-compressing the narrowband CDMA signal to form a wideband CDMA signal;

transmitting the wideband CDMA signal in a time-compressed burst.

28. The method of claim 27, further comprising the steps of:

receiving the time-compressed burst and time expanding the time-compressed burst to reform a narrowband CDMA signal; and

processing the restored narrowband CDMA signal to restore the information signals.

29. A method of communicating between at least one first station and plurality of second stations using Code Division Multiple Access including:

selecting at said first station a frequency channel, timeslot and power level to be used for transmitting to each of said second stations a respective CDMA signal such that the power levels of signals selected to be transmitted using the same frequency and timeslot are spread over a predetermined dynamic range;

adding together said CDMA signals selected to be transmitted on the same frequency and timeslot using weighting factors corresponding to the selected power levels of the CDMA signals to form a sum signal;

time-compressing said sum signal for transmission in the selected timeslot and modulating the time-compressed signal for transmission on the selected frequency channel.

30. The method of claim 29, wherein said predetermined dynamic range defines a maximum difference in power level between a highest power CDMA signal and a lowest power CDMA signal.

31. The method of claim 29, wherein the power levels are spread such that each timeslot contains a substantially even distribution of low and high power signals.

32. The method of claim 29, wherein in each timeslot on the same frequency channel, a total transmitted power is substantially equal.

33. The method of claim 32, wherein on each frequency channel, the total transmitted power is substantially equal.

34. The method of claim 29, in which said first station is a base station serving a cell in a cellular mobile communications network.

35. The method of claim 29, wherein a first base station in a first cell transmits a relatively high total transmitted power on a first frequency, and a second base station in a second cell adjacent to the first cell transmits a relatively low total transmitted power on the first frequency.