Broadcasting with mixed delay demands

Abstract

Consider the problem of simultaneously transmitting two data streams over a slow fading point-to-point channel, where the transmitter has no knowledge of the channel state information (CSI) while the receiver has perfect CSI. Two classes of data are transmitted: delay constrained (DC), restricted to be decoded shortly after receipt; and non delay constrained (NDC) which may use long codewords exploiting the channel ergodicity. A previous work characterized a setting, without cooperation between encoders of the different streams. This work studies the case of encoders cooperation. Rate region for the DC vs. NDC streams is obtained by providing achievable lower bounds, and tight outer bounds. Two main cooperative encoding schemes are considered. The first scheme uses short block Dirty Paper Coding (DPC) of the DC stream against the NDC as codeword, per DC block. Numerical results show that the first scheme does not improve the non-cooperative encoding (NCE) rate region. In a second scheme the notion of Dirty Notes Coding (DNC) is introduced, where DNC is encoded against genie aided DC data, providing a tight upper bound for the rate region.