Method of OFDM communication using superposition coding
View Patent ↗Improvements are provided in an OFDM network that uses superposition coding. A broadcast signal and e.g. a unicast signal are each subjected to OFDM modulation including processing by an IDFT, combined, and transmitted using non-orthogonal transmission resources. In one approach, the respective signals are combined after instead of before the IDFT processing. In specific examples, a respective cyclic prefix is appended to each signal after the IDFT processing but before the respective signals are combined. In another approach, a broadcast pilot signal and e.g. a unicast pilot signal are transmitted concurrently with the broadcast and unicast information signals. The pilot signals are transmitted using the same time and subcarrier resources, but are made more distinguishable by combining each with a respective scrambling or spreading code. In specific examples, embodiments, the unicast pilot signal is used for estimating the data rate for transmission of further unicast information signals.
1. A method of signal processing in a receiver configured to process signals at least at a sample level and a symbol level, comprising:
sampling an incoming wireless signal;
subjecting the sampled signal to discrete Fourier transform (DFT) processing, thereby to obtain a composite symbol-level signal;
recovering a first block of information from the composite symbol-level signal;
from the recovered first block of information, regenerating at the sample level a first estimate of that portion of the sampled incoming signal that is attributable to the first block of information;
at the sample level, subtracting the first estimate from the sampled incoming signal, thereby to provide a second estimate of that portion of the sampled incoming signal that is attributable to a second block of information;
subjecting the second estimate to DFT processing, thereby to obtain a further symbol-level signal; and
recovering the second block of information from the further symbol-level signal.
2. The method of claim 1 , further comprising:
removing a first cyclic prefix from the sampled signal before subjecting the sampled signal to DFT processing; and
removing a second cyclic prefix from the second estimate before subjecting the second estimate to DFT processing.
3. The method of claim 1 , wherein the sampled incoming signal comprises a broadcast superimposed with a unicast or multicast, one of said first and second blocks of information belongs to the broadcast, and the other of said first and second blocks of information belongs to the unicast or multicast, and the method further comprises:
obtaining from the sampled incoming signal a unicast or multicast pilot signal; and
from the unicast or multicast pilot signal, computing rate information for a subsequent unicast or multicast transmission.
4. A method of signal processing in a receiver configured to process signals at least at a sample level and a symbol level, comprising:
sampling an incoming wireless signal;
subjecting the sampled signal to discrete Fourier transform (DFT) processing, thereby to obtain a composite symbol-level signal and a composite pilot signal;
combining the composite pilot signal with a spreading or scrambling code, thereby to recover a first pilot signal;
using the recovered first pilot signal to recover a first block of information from the composite symbol-level signal;
recovering at least a second pilot signal from the composite pilot signal; and
recovering at least a second block of information, using the recovered pilot signals and the recovered first block of information.
5. The method of claim 4 , wherein recovering the second pilot signal comprises subtracting the recovered first pilot signal from the composite pilot signal.
6. The method of claim 4 , wherein recovering the second block of information comprises:
regenerating a first estimate of that portion of the composite symbol-level signal that is attributable to the first block of information, using the recovered first block of information and the recovered first pilot signal;
subtracting the first estimate from the composite symbol-level signal, thereby to provide a second estimate of that portion of the composite symbol-level signal that is attributable to the second block of information; and
using the recovered second pilot signal to recover the second block of information from the second estimate.
7. The method of claim 4 , wherein the sampled incoming signal comprises a broadcast superimposed with a unicast or multicast, one of said first and second blocks of information belongs to the broadcast, the other of said first and second blocks of information belongs to the unicast or multicast, one of said first and second pilot signals is a broadcast pilot signal, and the other of said first and second pilot signals is a unicast or multicast pilot signal, and the method further comprises:
from the unicast or multicast pilot signal, computing rate information for a subsequent unicast or multicast transmission.