Receiver for receiving embedding OFDM in an CDMA systems
View Patent ↗Systems and methods of combining OFDM and CDMA signals are provided. An OFDM packet data channel is overlaid over CDMA transmissions. The channel is scheduled slotwise between multiple users. In some embodiments, there is a CDMA packet data channel which is scheduled together with the OFDM packet data channel.
1. A receiver comprising:
an analog-to-digital (A/D) converter for producing a sequence of samples of a received signal;
a Code Division Multiple Access (CDMA) demodulator for performing CDMA demodulation upon the sequence of samples;
an Orthogonal Frequency Division Multiplexing (OFDM) demodulator for performing OFDM demodulation upon the sequence of samples; and
the receiver for receiving a control channel identifying for a given slot whether or not the receiver is scheduled during the slot and the receiver demodulates a given OFDM slot only if scheduled during the slot.
2. The receiver according to claim 1 ,
for determining a CDMA channel quality indicator for CDMA and an OFDM channel quality indicator for OFDM;
for providing a feed back of a better of the CDMA channel quality indicator and the OFDM channel quality indicator; and
if the CDMA channel quality is better, use CDMA mode to demodulate a next slot for the receiver; or
if the OFDM channel quality is better, use OFDM mode to demodulate a next slot for the receiver.
3. The receiver according to claim 1
for performing CDMA demodulation by descrambling at least one common channel, de-spread and perform soft-de-mapping and forward error correction (FEC) decoding during which the OFDM content will be substantially converted to additive white gaussian noise (AWGN); and
for demodulating the OFDM slots by generating an interference term due to a CDMA component of the received signal, subtract the interference term from the received signal, and perform OFDM demodulation on a remaining signal.
4. The receiver according to claim 3 for generating the interference term by:
de-scrambling, de-spreading, soft de-mapping and FEC decoding (or hard decision), re-encoding, re-spreading, re-scrambling, convolving with an estimated channel response.
5. The receiver according to claim 1 for using OFDM pilots to generate channel estimates for both OFDM and CDMA.
6. The receiver according to claim 1 for performing channel estimation by:
performing a fast fourier transform (FFT) on the sequence of samples;
performing a first transformation on a set of samples collectively output by the FFT;
performing a per sub-carrier transformation on an output of the first transformation;
performing a second transformation on outputs of the per sub-carrier transformations collectively to produce an OFDM channel estimate; and
performing an inverse fast fourier transform (IFFT) on the OFDM channel estimate to produce a time domain channel estimate for CDMA finger searching.
7. The receiver according to claim 1 for using CDMA pilots for channel estimation for both CDMA and OFDM.
8. The receiver according to claim 1 for performing channel estimation by:
performing CDMA searching and correlation to produce a time-domain channel response;
performing a fast fourier transform (FFT) on the time domain channel response;
performing a first transformation on a set of samples collectively output by the FFT;
performing a per sub-carrier transformation on an output of the first transformation;
performing a second transformation on outputs of the per sub-carrier transformations collectively to produce an OFDM channel estimate; and
performing an inverse fast fourier transform (IFFT) on the OFDM channel estimate to produce a time domain channel estimate for CDMA finger searching.
9. The receiver according to claim 1 for receiving a signal on multiple carriers, the receiver comprising an FFT function for performing a fast fourier transform (FFT) for sub-carriers spanning the multiple carriers.
10. A receiver comprising:
an analog-to-digital (A/D) converter for producing a sequence of samples of a received signal;
a Code Division Multiple Access (CDMA) demodulator for performing CDMA demodulation upon the sequence of samples by descrambling at least one common channel, de-spread and perform soft-de-mapping and forward error correction (FEC) decoding during which the OFDM content will be substantially converted to additive white gaussian noise (AWGN);
an Orthogonal Frequency Division Multiplexing (OFDM) demodulator for performing OFDM demodulation upon the sequence of samples by generating an interference term due to a CDMA component of the received signal, subtract the interference term from the received signal, perform OFDM demodulation on a remaining signal; and
the receiver for receiving a control channel identifying for a given slot whether or not the receiver is scheduled during the slot and the receiver demodulates a given OFDM slot only if scheduled during the slot.