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...s are i.i.d. ∼ CN (0, 1). It is assumed that H is random, but constant over T symbol durations. Let γs denote SNR per symbol, which is defined as γs := E [ |(sk)i|2 ] /σ2n where (sk)i is the ith component of sk. Let Ns denote the number of symbols packed within a spacetime codeword S. The spatial multiplexing rate is defined as Ns/T . We assume that H is known at the receiver, but not known at the transmitter. Next, we briefly present the outage probability expression of the space-time code, which is derived in [2], for any given piecewise-linear diversity-multiplexing tradeoff (DMT) function [3]. Consider a space-time code whose DMT characteristic function is given by d(r) = v − ur, for α ≤ r ≤ β (α > 0) (2) where d(r) ≥ 0, and u ≥ 0 and v ≥ 0 are real constants. Let Pout(γs) denote the outage probability for the space-time code whose DMT is given by (2). In [2], it is shown that, as γs → ∞, Pout(γs) can be expressed as Pout(γs) = kd ( 2R kr )u 1 γvs for ( 2R kr ) 1 β ≤ γs ≤ ( 2R kr ) 1 α (3) where R is the spectral efficiency (bits/s/Hz), and kr and kd are arbitrary positive constants. Consider two space-time codes which have linear DMT characteristics as follows: d1(r) = v1 − u1r a...

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...ennas is n2 is used (i.e., n2×n2 systems). Suppose that n1 < n2. Then, from the given results, we have P ∗out,1 > P ∗ out,2. (16) Based on (16), the outage probabilities of V-BLAST and OSTBC are qualitatively depicted in Fig. 1. Suppose that a target outage probability, Pout,T , is smaller than P ∗out,1 but greater than P ∗out,2. Then, from Fig. 1, it is seen that OSTBC is preferable to V-BLAST for an n1×n1 MIMO system, whereas V-BLAST is preferable for an n2 × n2 system (n1 < n2). Note that DMT characteristics are not influenced by spatial correlation or line-of-sight (LOS) signal components [5], [6]. In other words, the DMT function for spatially correlated Rayleigh fading or Rician fading is identical to that for i.i.d. Rayleigh fading. From this, it follows that the analysis of the crossover points is also valid over those channels at high SNR. IV. SPACE-TIME CODING OF A LAYERED BITSTREAM We exploit the analysis in the previous section to design a MIMO system for the transmission of the applications which need unequal target error rates in their bitstream. To begin, we briefly present the transmission of layered multimedia sources. Progressive encoders employ a mode of transmissio...

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... is n2 is used (i.e., n2×n2 systems). Suppose that n1 < n2. Then, from the given results, we have P ∗out,1 > P ∗ out,2. (16) Based on (16), the outage probabilities of V-BLAST and OSTBC are qualitatively depicted in Fig. 1. Suppose that a target outage probability, Pout,T , is smaller than P ∗out,1 but greater than P ∗out,2. Then, from Fig. 1, it is seen that OSTBC is preferable to V-BLAST for an n1×n1 MIMO system, whereas V-BLAST is preferable for an n2 × n2 system (n1 < n2). Note that DMT characteristics are not influenced by spatial correlation or line-of-sight (LOS) signal components [5], [6]. In other words, the DMT function for spatially correlated Rayleigh fading or Rician fading is identical to that for i.i.d. Rayleigh fading. From this, it follows that the analysis of the crossover points is also valid over those channels at high SNR. IV. SPACE-TIME CODING OF A LAYERED BITSTREAM We exploit the analysis in the previous section to design a MIMO system for the transmission of the applications which need unequal target error rates in their bitstream. To begin, we briefly present the transmission of layered multimedia sources. Progressive encoders employ a mode of transmission so ...

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...exploited to simplify the computational complexity involved with the optimal space-time coding of a layered bitstream. I. INTRODUCTION The demand for multimedia services has invoked much research on cross-layer design. In this paper, we study the optimal design of a low-complex open-loop multiple-input multiple-output (MIMO) system for the transmission of layered (or progressive) multimedia sources. First, we compare the outage probabilities of vertical Bell Labs spacetime architecture (V-BLAST) with a minimum mean-square error (MMSE) receiver and orthogonal space-time block codes (OSTBC). In [1], the authors analyzed how the crossover point of the outage probabilities of the two space-time codes behaves as spectral efficiency increases. On the other hand, in this paper, we analyze the behavior from the viewpoint of the number of antennas. More specifically, it is shown that as we increase the number of transmit antennas which is set to be equal to that of receive antennas, the crossover point of the outage probability curves monotonically decreases. The results hold for an arbitrarily given spectral efficiency, and propagation channels such as spatially correlated Rayleigh or Rician ...