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, comprising:
providing at least a first and a second block of information;
mapping at least said first and second information blocks to respective blocks of modulation symbols;
subjecting said blocks of modulation symbols to inverse discrete Fourier transform (IDFT) processing, thereby to provide at least first and second respective OFDM symbols which share at least some frequency subchannels in at least some transmission timeslots;
appending a respective cyclic prefix to each of at least the first and second OFDM symbols;
after said appending step, combining said OFDM symbols, thereby to provide a composite signal for transmission in which the respective OFDM symbols are not mutually orthogonal; and
transmitting the composite signal;
wherein the cyclic prefix appended to the first OFDM symbol has a different length from the cyclic prefix appended to the second OFDM symbol.
2. A method, comprising:
providing at least a first and a second block of information;
mapping at least said first and second information blocks to respective blocks of modulation symbols;
subjecting said blocks of modulation symbols to inverse discrete Fourier transform (IDFT) processing, thereby to provide at least first and second respective OFDM symbols which share at least some frequency subchannels in at least some transmission timeslots;
combining said OFDM symbols, thereby to provide a composite signal for transmission in which the respective OFDM symbols are not mutually orthogonal;
before said combining step, providing at least a first and a second pilot signal;
subjecting said at least first and second pilot signals to IDFT processing in respective concert with said at least first and second blocks of modulation symbols, thereby to include said pilot signals in the composite signal for transmission; and
transmitting the composite signal.
3. The method of claim 2 , wherein the composite signal comprises a broadcast superimposed with a unicast or multicast, one of said first and second blocks of modulation symbols belongs to the broadcast, the other of said first and second blocks of modulation symbols belongs to the unicast or multicast, one of said first and second pilot signals is a broadcast pilot signal, the other of said first and second pilot signals is a unicast or multicast pilot signal, and the method further comprises:
from a terminal to which the composite signal was transmitted, receiving rate information based on the unicast or multicast pilot signal; and
using the rate information to determine the data rate for a subsequent unicast or multicast transmission.
4. A method, comprising:
providing at least a first and a second block of information;
mapping at least said first and second information blocks to respective blocks of modulation symbols;
subjecting said blocks of modulation symbols to inverse discrete Fourier transform (IDFT) processing, thereby to provide at least first and second respective OFDM symbols which share at least some frequency subchannels in at least some transmission timeslots;
combining said OFDM symbols, thereby to provide a composite signal for transmission in which the respective OFDM symbols are not mutually orthogonal; and
transmitting the composite signal;
wherein the composite signal comprises a broadcast superimposed with a unicast or multicast, one of said first and second OFDM symbols belongs to the broadcast, and the other of said first and second OFDM symbols belongs to the unicast or multicast.
5. The method of claim 4 , wherein the broadcast is a retransmission of a previous broadcast, but the unicast or multicast is new.
6. A method, comprising:
providing at least a first and a second block of information and at least a first and a second respective pilot signal;
combining said at least first and second pilot signals with respective spreading or scrambling codes, thereby to provide at least first and second spread pilot signals;
combining said spread pilot signals, thereby to provide a composite pilot signal;
deriving a composite OFDM symbol from the first and second blocks of information and the composite pilot signal; and
transmitting the composite OFDM symbol.
7. The method of claim 6 , wherein deriving the composite OFDM symbol comprises:
mapping at least said first and second information blocks to respective blocks of modulation symbols;
combining said blocks of modulation symbols, thereby to provide a composite symbol-level signal; and
in concert, subjecting said composite symbol-level signal and said composite pilot signal to inverse discrete Fourier transform (IDFT) processing.
8. The method of claim 7 , wherein the composite OFDM symbol comprises a broadcast superimposed with a unicast or multicast, one of said first and second information blocks belongs to the broadcast, and the other of said first and second information blocks belongs to the unicast or multicast.
9. The method of claim 8 , wherein one of said first and second pilot signals is a broadcast pilot signal, the other of said first and second pilot signals is a unicast or multicast pilot signal, and the method further comprises:
from a terminal to which the composite OFDM symbol was transmitted, receiving rate information based on the unicast or multicast pilot signal; and
using the rate information to determine the data rate for a subsequent unicast or multicast transmission.
10. The method of claim 8 , wherein the broadcast is a retransmission of a previous broadcast, but the unicast or multicast is new.