Programmable transceiver structure of multi-rate OFDM-CDMA for wireless multimedia communications

• US 20030026200A1
• Filed: 09/12/2001
• Published: 02/06/2003
• Est. Priority Date: 04/20/2001
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: MediaTek, Inc.
• Inventors: Chen, Kwang-Cheng, Fu, Po-Wei
• Granted Patent: US 7,035,201 B2
• Time in Patent Office: Days
• US Class Current: 370/208
• CPC Class Codes: H04B 1/692 Hybrid techniques using combinations of two or more spread spectrum techniques
• CPC Class Codes: H04L 5/026 using code division

Abstract

Two multi-rate transmission schemes, multi-code (MC) and variable-spreading-length (VSL) code, for realizing multimedia communications on three types of OFDM-CDMA systems are proposed. These systems can be integrated into a programmable structure such that the operation can be controlled and adjusted by system parameters and thus the transceiver can be used in different systems without changing the fundamental hardware and software architecture, which serves the trend of software-radio for future application. A transceiver architecture of multi-rate OFDM-CDMA systems is illustrated and showed its programmability such that the general system can operate under different scenarios with a common hardware structure and reconfigure by software implementation.

Claims

1. A method for multiplexing and multiple accessing a multi-rate OFDM-CDMA system with an input data stream having a data rate of a predetermined value m, said m being a multiple of a basic rate and said multi-rate OFDM-CDMA system having a plurality of predetermined spreading codes and a plurality of orthogonal carrier, said input data stream having a selected number of data being m×

P, and each data representing a symbol having a predetermined sample duration, said method comprising the steps of;

(a1) multiplexing said input data stream into m effective data sub-streams each having a data rate equal to said basic rate and having P data;

(a2) performing an OFDM operation on each of said m effective data sub-streams; and

(a3) performing a CDMA operation on each of said m effective data sub-streams being performed with OFDM operation.

2. The method of claim 1, wherein said step (a2) further comprises the steps of:

(b1) serial-to-parallel converting each of said m data sub-streams into P parallel data in each sub-stream; and

(b2) copying said representative symbol of each data into F branches indicating from a first branch to a Fth branch, wherein F is a constant spreading factor of said plurality of spreading codes.

3. The method of claim 2, wherein said step a(3) further comprises the step of utilizing a frequency domain spreading in said CDMA operation further comprising the steps of:

(c1) spreading said representation symbol at each of said F branches as a spread symbol in the frequency domain by utilizing a predetermined bit in a selective one of said plurality of spreading codes, thereby, for each effective data sub-stream, there being P×

F spread symbols which are indicated as a first, a second, and a P×

F^th spread sub-branches, respectively;

(c2) combining i^th spread symbol of each of the effective data sub-stream as an i^th combined symbol, where i is from 1 to P×

F;

(c3) modulating P×

F orthogonal carriers by said P×

F combined symbol as modulated sub-carriers; and

(c4) transmitting said plurality of modulated sub-carriers, wherein a frequency difference of two adjacent carriers of said plurality of P×

F orthogonal carriers is an inverse of the product of said P multiplied with said symbol duration.

4. The method of claim 3, wherein in step (c2), said modulation performed on orthogonal carriers is executed by using inverse discrete Fourier transform.

5. The method of claim 2, wherein said step (a3) further comprises the step of utilizing a time spreading in said CDMA operation having the steps of:

(d1) spreading said representation symbol of each of said P data in time domain so as to acquire a spread symbol by utilizing a selected one of said plurality of spreading codes via cyclically multiplying said codes;

thereby, for each effective data sub-stream, there being P spread symbols which are indicated as a first, a second, and a P th spread sub-branches, respectively;

(d2) combining ith spread symbol of each of the effective data sub-streams as an ith combined symbols, where i is from 1 to P;

(d3) modulating P orthogonal carriers by said P combined symbols as modulated sub-carriers; and

(d4) transmitting said modulated sub-carriers.

6. The method of claim 5, wherein in step (d2), inverse discrete Fourier transform is utilized to perform said modulation on orthogonal carriers.

7. The method of claim 2, wherein said step a(3) further comprises the step of utilizing a time spreading in said CDMA operation having the steps of:

,

(e1) spreading said representation symbol of each of said P data in time domain so as to acquire a spread symbol by utilizing one selected spreading code of said plurality of spreading codes via cyclically multiplying said codes;

thereby, for each effective data sub-stream, there being P spread symbols which are indicated as a first, a second, and a P th spread sub-symbol, respectively;

Tb (e2) combining ith spread symbol of each of the effective data sub-streams as an ith combined sub-symbols, where i is from 1 to P;

(e3) modulating P orthogonal carriers by said P combined symbols as modulated sub-carriers wherein frequency difference of two adjacent carriers is an inverse of the product of P multiplied with a symbol duration of said data stream with a basic rate; and

(e4) transmitting said modulated sub-carriers.

8. The method of claim 7, wherein in step (e2), NOC-IDFT is utilized to perform said modulation by orthogonal carriers.

9. A method for multiplexing and multiple accessing a multi-rate OFDM-CDMA system with an input data stream having a data rate of a predetermined value m, said m being a multiple of a basic rate and said multi-rate OFDM-CDMA system having a plurality of predetermined spreading codes and a plurality of orthogonal carrier;

said input data stream having a selected number of data, being m×

P, and each data representing a symbol having a predetermined sample duration, said method comprising the steps of;

(A1) serial-to-parallel converting each data stream into P×

m data; and

(A2) copying each of said symbols into F/m branches , wherein F/m is a constant length of said plurality of spreading codes, and F is selected to cause F/m to be an integer;

(A3) spreading said symbol at each branch in frequency domain by a predetermined bit of a selective one of said spreading codes so as to acquire an spread branch;

(A4) modulating all said spread branch by a plurality of orthogonal carriers and combining all the modulated parallel signals for transmission;

wherein frequency difference of two adjacent carriers is an inverse of the product of P multiplied with a symbol duration of said data stream with basic rate.

10. The method of claim 9, wherein in step (A4), inverse discrete Fourier transform is utilized to perform said modulation on orthogonal carriers.

11. A method for multiplexing and multiple accessing a multi-rate OFDM-CDMA system with an input data stream having a data rate of a predetermined value m, said m being a multiple of a basic rate and said multi-rate OFDM-CDMA system having a plurality of predetermined spreading codes each having length F/m and a plurality of orthogonal carriers, said input data stream having a selected number of data being m×

p, and each data representing a symbol having a predetermined sample duration, said method comprising the steps of;

(C1) serial-to-parallel converting each data stream into P data sub-streams; and

(C2) spreading each sub-stream in time domain by cyclically multiplying said same spread codes so as to acquire P spreading sub-streams which are indicated from a first spread sub-stream to p^th spread sub-stream;

wherein F is selected so that F/m is an integer, said F/m is a constant spreading factor of the spread spectrum operation of said system.

12. The method of claim 11, further comprising a step after step (C2) of modulating said P orthogonal carriers by said P spread sub-streams and combining all the P parallel signals for transmission.

13. The method of claim 12, wherein inverse discrete Fourier transform is utilized to perform said modulation.

14. The method of claim 11, further comprising a step after step (C2) of modulating said P orthogonal carriers by said P spread sub-streams and combining all the P parallel signals for transmission, wherein frequency difference of two adjacent carriers is an inverse of a result of P multiplied with a symbol duration of said data stream with basic rate.

15. The method of claim 14, wherein NOC-IDFT is utilized to perform said modulation on carriers.

16. A programmable OFDM-CDMA transmitter for transmitting both multi-rate signals and single rate signals of three access systems, MC-CDMA, MC-DS-CDMA, MT-CDMA;

said programmable OFDM-CDMA transmitter receiving an input data stream with a data rate of m being a multiple of a basic rate and being operated in a plurality of pre-selected modes containing a multi-code assessing mode and a VSL-code access mode and each mode including a plurality of scenarios containing an MC-CDMA scenario, a MC-DS CDMA scenario, and a MT-CDMA scenario;

said input data stream having a selected number of data, P, further said OFDM-CDMA transmitter having a plurality of spreading codes with a predetermined spreading factor corresponding to a plurality of spreading codes and spreading factors in said OFDM-CDMA transmitter and each data representing a symbol having a predetermined sample duration, comprising;

an effective user splitter for determining the number of enabled sub-streams after receiving said data stream responsive said mode of said input data stream, splitting said data stream into a plurality of data sub-streams and outputting said data sub-streams;

a serial to parallel converter having a serial to parallel ratio for receiving said data sub-stream from said effective user splitter and determining the number of parallel outputs responsive to said serial to parallel ratio and serial-to-parallel converting each data sub-stream into a plurality of data; and

outputting said data;

a copying and spreading unit for determining the number of enabled branches responsive to said spreading factor, and receiving said data outputted from said serial to parallel converter for copying said symbol representing data outputted from said serial-to-parallel converter into a plurality of branches and spreading said symbol representing said data at each branch as a spread branch;

outputting said spread branches;

a zero padding and IFFT processor for receiving said spread branches outputted from said copying and spreading unit for determining the number of operation points in IFFT for each scenario responsive to said spreading factor, and performing a regular-zero padding to said branch for executing a regular IFFT operation responsive to a multi-rate MC-CDMA, a multi-rate MC-DS-CDMA or performing a circular-shift padding for an NOC-IFFT operation responsive to a multi-rate MT-CDMA, thereby, acquiring a transformed symbol, and outputting said transformed symbols;

a parallel to serial converter for receiving said transformed symbols from said zero padding and IFFT processor and determining said enabled input branches thereof and a conversion ratio at different scenarios, converting said transformed symbol into a serial data stream, and outputting said serial data stream; and

a digital to analog converter for receiving said serial data stream from said parallel to serial converter, converting said serial data stream into an analog stream for transmission, and outputting said analog stream.

17. The programmable OFDM-CDMA transmitter of claim 16, wherein as said transmitter is operated on said multi-code access mode, said effective user splitter multiplexes said data stream into a plurality of sub-streams with each sub-stream having a basic rate.

18. The programmable OFDM-CDMA transmitter of claim 16, wherein said effective user splitter, as said transmitter is operated on said VSL mode, just forward said data stream to said serial to parallel converter.

19. The programmable OFDM-CDMA transmitter of claim 16, wherein in said MC-CDMA of said VSL mode, the number of parallel output branches from said serial-to-parallel converter are set to be m×

P;

otherwise, the number of parallel outputting branch is P.

20. The programmable OFDM-CDMA transmitter of claim 16, wherein if said scenario is MC-CDMA, said enabled branch is F for said multi-code access and F/m for said VSL access;

and if said scenario is MT-CDMA, the number of branch is 1 for both said multi-code assessing mode and said VSL code accessing mode.

21. The programmable OFDM-CDMA transmitter of claim 16, wherein for MC-DS-CDMA and MT-CDMA, a cyclical multiplying by corresponding spreading codes (time-domain spreading) on each branch is set;

for MC-CDMA mode, signal on each branch is spread by multiplying one corresponding bit of spreading codes (frequency-domain spreading).

22. The programmable OFDM-CDMA transmitter of claim 16, wherein said digital to analog converter supports an input data rate higher than any possible sampling rate.

23. A programmable OFDM-CDMA receiver for receiving an input data sequence, which are OFDM-CDMA analog signals from an OFDM-CDMA transmitter through a plurality of communication channels;

being operated in plurality of pre-selected modes containing a multi-code assessing mode and a VSL code and each mode serving a plurality of scenarios an MC-CDMA scenario, a MC-DS CDMA scenario, and a MT-CDMA scenario and having a plurality of predetermined despreading codes with a predetermined despreading factors corresponding to a plurality of spreading codes in said OFDM-CDMA transmitter, comprising;

an analog to digital converter for controlling a sample rate of said received OFDM-CDMA multiplexed signals including the number of input data utilized in following FFT operation in responsive to a selected scenario, converting input analog signals into a digital sequence and outputting said digital sequence;

a serial to parallel converter for receiving said digital sequence from said analog to digital converter and determining a ratio in serial to parallel conversion and the number of parallel outputs of said serial to parallel converter responsive to said selected scenario, converting said digital sequence outputted from said analog to digital converter into a plurality of parallel data and output said parallel data;

an FFT processor for receiving said parallel data from said serial to parallel converter;

performing an FFT operation to said parallel data to form a plurality of transformed data and outputting said plurality of transformed data;

a sample filter for receiving said plurality of transformed data outputted from said FFT processor, deciding regular filtering for said multi-rate MC-CDMA and multi-rate MC-DS-CDMA or circular-shift-filtering for said multi-rate MT-CDMA will be executed, controlling filtering of said plurality of transformed data after FFT to discard signals out of predetermined sub-bands, and determining enabled tapped-delay-lines;

wherein a pass window of sample filtering having a width equal to the number of sub-carriers is used in transmission;

a despreader for receiving outputs from said sample filter, dispreading each output of said sample filter in response to said selected scenario by multiplying a plurality of said despreading codes, and outputting a plurality of despreading data;

a sampler having an input from said despreader for determining a sampling rate for taking samples on each line at said dispreading process and outputting a plurality of sampled data;

wherein said sampling rate equals said OFDM symbol duration;

a detector having an input of said plurality of sampled data from said sampler for making a decision by combining these diversities based on a collection of samples from said sampler and outputting a detected sequence; and

a demultiplexer receiving said detected sequence from said detector for de-multiplexing the detected sequence in response to a selected multi-code mode so as to reconstruct an original data sequence from said OFDM-CDMA transmitter.

24. The programmable OFDM-CDMA receiver of claim 23, wherein said sample filter performs circular-shift-window filtering for MT-CDMA modes and regular sample filtering for MC-CDMA mode and MC-DS-CDMA mode.

25. The programmable OFDM-CDMA receiver of claim 23, wherein in said FFT processor and sample filter, FFT is operated with circular-shift-window filtering for MT-CDMA modes and with regular sample filtering for MC-CDMA and MC-DS-CDMA modes.

26. The programmable OFDM-CDMA receiver of claim 23, wherein said despreader has a tapped-delay-line (TDL) form and the number of enabled TDL equals a width of said pass window in said sample filter.

27. The programmable OFDM-CDMA receiver of claim 26, wherein said despreader determines the number of enabled tap and a time spacing of each tap for MC-CDMA modes, only one tap is needed and each line corresponds to one bit of said spreading codes;

for MC-DS-CDMA and MT-CDMA modes, the number of taps in each tapped-delay-line equals said spreading factor.