605 research outputs found

    Multifunctional MIMO systems: A combined diversity and multiplexing design perspective

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    In this treatise we investigate the design alternatives of different multiple-input multiple-output schemes while considering the attainable diversity gains, multiplexing gains, and beamforming gains. Following a brief classification of different MIMO schemes, where the different MIMO schemes are categorized as diversity techniques, multiplexing schemes, multiple access arrangements, and beamforming techniques, we introduce the family of multifunctional MIMOs. These multifunctional MIMOs are capable of combining the benefits of several MIMO schemes and hence attaining improved performance in terms of both their bit error rate as well as throughput. The family of multifunctional MIMOs combines the benefits of both space-time coding and the Bell Labs layered space-time scheme as well as those of beamforming. We also introduce the idea of layered steered space-time spreading, which combines the benefits of space-time spreading, V-BLAST, and beamforming with those of the generalized multicarrier direct sequence code-division multiple access concept. Additionally, we compare the attainable diversity, multiplexing, and beamforming gains of the different MIMO schemes in order to document the advantages of multifunctional MIMOs over conventional MIMO schemes

    Single-Symbol ML Decodable Distributed STBCs for Partially-Coherent Cooperative Networks

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    Space-time block codes (STBCs) that are single-symbol decodable (SSD) in a co-located multiple antenna setting need not be SSD in a distributed cooperative communication setting. A relay network with N relays and a single source-destination pair is called a partially-coherent relay channel (PCRC) if the destination has perfect channel state information (CSI) of all the channels and the relays have only the phase information of the source-to-relay channels. In this paper, first, a new set of necessary and sufficient conditions for a STBC to be SSD for co-located multiple antenna communication is obtained. Then, this is extended to a set of necessary and sufficient conditions for a distributed STBC (DSTBC) to be SSD for a PCRC, by identifying the additional conditions. Using this, several SSD DSTBCs for PCRC are identified among the known classes of STBCs. It is proved that even if a SSD STBC for a co-located MIMO channel does not satisfy the additional conditions for the code to be SSD for a PCRC, single-symbol decoding of it in a PCRC gives full-diversity and only coding gain is lost. It is shown that when a DSTBC is SSD for a PCRC, then arbitrary coordinate interleaving of the in-phase and quadrature-phase components of the variables does not disturb its SSD property for PCRC. Finally, it is shown that the possibility of {\em channel phase compensation} operation at the relay nodes using partial CSI at the relays increases the possible rate of SSD DSTBCs from 2N\frac{2}{N} when the relays do not have CSI to 1/2, which is independent of N

    On the MIMO Channel Capacity of Multi-Dimensional Signal Sets

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    In this contribution we evaluate the capacity of Multi-Input Multi-Output (MIMO) systems using multi-dimensional PSK/QAM signal sets. It was shown that transmit diversity is capable of narrowing the gap between the capacity of the Rayleigh-fading channel and the AWGN channel. However, since this gap becomes narrower when the receiver diversity order is increased, for higher-order receiver diversity the performance advantage of transmit diversity diminishes. A MIMO system having full multiplexing gain has a higher achievable throughput than the corresponding MIMO system designed for full diversity gain, although this is attained at the cost of a higher complexity and a higher SNR. The tradeoffs between diversity gain, multiplexing gain, complexity and bandwidth are studied
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