Subspace inversion symbol energy adaptation in MIMO Rayleigh channel with zero outage probability

Our paper solves the problem of symbol energy adaptation in a MIMO Rayleigh block fading channel with the constant target rate criterion. An equal number of transmitting and receiving antennas is considered. We treat the problem where a direct total inversion is impossible due to its infinite energy requirement. It is shown that truncated channel inversion demonstrates a high transmission outage probability. This can be solved by a novel subspace total inversion strategy. The subspace is obtained by subtracting the weakest eigenmode of the channel. It is shown that this subspace can be totally inverted and thus it has no transmission outage. The long-term mean capacity is shown to be very close to the truncated channel inversion strategy. This subspace approach has lower sustained throughput without outage (useful for BLAST-like schemes) compared to the higher burst like throughput with high outage probability in the truncated inversion case.