Spatial Multiplexing Architectures with Jointly Designed Rate-Tailoring and Ordered BLAST Decoding - Part I: Diversity-Multiplexing Tradeoff Analysis

The V-BLAST (vertical Bell Labs layered Space- Time) architecture involves independent coding/decoding per antenna (layer) with equal rate and power per antenna and a fixed order of nulling/canceling decoding but is known to suffer from poor performance; for example, in a multi-input multioutput (MIMO) Rayleigh fading channel with Mt transmit and Mr receive antennas (M
_r
⩾ M
_t
), the diversity-multiplexing gain (D-M) tradeoff is just (M
_r
- M
_t
+1)(1 - r/Mt) for r ε [0,Mt]. There are two remedies available, namely, (i) channel-dependent ordered decoding at the receiver and (ii) allocation of rates and powers across the transmit antennas. However, the former doesn't improve the D-M tradeoff curve and while the latter does (with maximum diversity gain Mr and maximum multiplexing gain Mt), its tradeoff curve is still significantly inferior compared to the D-M tradeoff curve of the optimum (unconstrained) MIMO architecture. In this two-part paper, it is shown that a dramatically better D-M tradeoff and error (e.g. outage) probability can be obtained if the two remedies, i.e., ordered BLAST decoding and rate/power allocation, are judiciously combined. Indeed, a framework is developed for jointly designing channel-dependent ordered decoding at the receiver and decoding order-dependent rate/power allocation at the transmitter. The framework encompasses a large class of new spatial multiplexing architectures (SMAs). In this part, an upper bound to the D-M tradeoff for this class is obtained and found to be quite close to the optimal D-M tradeoff of the MIMO channel. Two special SMAs are proposed corresponding to two different decoding orderings. One is called the Norm ordering Rate Tailored SMA (NRT-SMA), and the other is called the Greedy ordering Rate Tailored SMA (GRT-SMA).