Modulation-mode and power assignment in SVD-equalized MIMO systems

Abstract

Existing bit loading and transmit power allocation techniques are often optimized for maintaining both a fixed transmit power and a fixed target bit-error rate while attempting to maximize the overall data-rate. However, delay-critical real-time interactive applications, such as voice or video transmission, may require a fixed data rate. In this contribution the number of activated layers in a multiple input multiple output (MIMO) system and the number of bits per symbol along with the appropriate allocation of the transmit power are jointly optimized under the constraint of a given fixed data throughput. Our results show that in order to achieve the best bit-error rate, not necessarily all MIMO layers have to be activated. .

Modulation-Mode Assignment for SVD-Assisted Multiuser Mimo Systems With Correlation

“…In order to avoid any signalling overhead, fixed transmission modes are used in this contribution regardless of the channel quality (Ahrens and Lange, 2008). However, the user-specific BER of the uncoded MIMO system is dominated by the specific layers having the lowest SNR's.…”

“…The power to be allocated to each activated MIMO layer at the time m can be shown to be calculated as follows (Ahrens and Lange, 2008): …”

“…However, in order to comply with the demand on increasing available data rates in particular in wireless technologies, systems with multiple transmit and receive antennas, also called MIMO systems, have become indispensable and can be considered as an essential part of increasing both the achievable capacity and integrity of future generations of wireless systems (Kühn, 2006). Besides, single-user MIMO transmission schemes for both non-frequency and frequency selective MIMO channels have attracted a lot of attention and reached a state of maturity (Kühn, 2006;Ahrens and Lange, 2008). By contrast, MIMO-aided multiple-user systems require substantial further research where both multiuser as well as multi-antenna interferences have to be taken into account.…”

Modulation-Mode Assignment in SVD-Assisted Multiuser Mimo-Ofdm Systems

“…which is often used as a quality parameter (Ahrens and Lange, 2008). The relationship between the signal-to-noise ratio ρ = U 2 A /U 2 R and the bit-error probability evaluated for AWGN channels and M-ary Quadrature Amplitude Modulation (QAM) is given by (Proakis, 2000) …”

“…However, as shown in (Ahrens and Lange, 2009) a vector quantizer (VQ) can be used to keep the signalling overhead moderate. Here, a VQ for the power allocation parameters instead of the singular values guarantees a better adaption at a given codebook size, since the power level vectors has less or equal dimensions than the singularvalue vectors (Ahrens and Lange, 2009). Moreover, its elements are much smaller digits ranged from 0 to 1, rather than from 0 to +∞ in the singular-value vector case.…”