Square Complex Orthogonal Designs with Low PAPR and Signaling Complexity

Space-Time Block Codes from square complex orthogonal designs (SCOD) have been extensively studied and most of the existing SCODs contain large number of zero. The zeros in the designs result in high peak-to-average power ratio (PAPR) and also impose a severe constraint on hardware implementation of the code when turning off some of the transmitting antennas whenever a zero is transmitted. Recently, rate 1/2 SCODs with no zero entry have been reported for 8 transmit antennas. In this paper, SCODs with no zero entry for $2^a$ transmit antennas whenever $a+1$ is a power of 2, are constructed which includes the 8 transmit antennas case as a special case. More generally, for arbitrary values of $a$, explicit construction of $2^a\times 2^a$ rate $\frac{a+1}{2^a}$ SCODs with the ratio of number of zero entries to the total number of entries equal to $1-\frac{a+1}{2^a}2^{\lfloor log_2(\frac{2^a}{a+1}) \rfloor}$ is reported, whereas for standard known constructions, the ratio is $1-\frac{a+1}{2^a}$. The codes presented do not result in increased signaling complexity. Simulation results show that the codes constructed in this paper outperform the codes using the standard construction under peak power constraint while performing the same under average power constraint.Comment: Accepted for publication in IEEE Transactions on Wireless Communication. 10 pages, 6 figure

Transmit-Diversity-Assisted Space-Shift Keying for Colocated and Distributed/Cooperative MIMO Elements

Space Shift Keying (SSK) modulation is a recently proposed MIMO technique, which activates only a single transmit antenna during each time slot and uses the specific index of the activated transmit antenna to implicitly convey information. Activating a single antenna is beneficial in terms of eliminating the inter-channel interference, and mitigates the peak-to-mean power ratio, while avoiding the need for synchronisation among transmit antennas. However, this benefit is achieved at a sacrifice, since the transmit diversity gain potential of the multiple transmit antennas is not fully exploited in existing SSK assisted systems. Furthermore, a high SSK throughput requires the transmitter to employ a high number of transmit antennas, which is not always practical. Hence, we propose four algorithms, namely open-loop Space Time Space Shift Keying (ST-SSK), closed-loop feedback-aided phase rotation, feedback-aided power allocation, and cooperative ST-SSK, for the sake of achieving a diversity gain. The performance improvements of the proposed schemes are demonstrated by Monte-Carlo simulations for spatially independent Rayleigh fading channels. Their robustness against channel estimation errors is also considered. We advocate the proposed ST-SSK techniques, which are capable of achieving a transmit diversity gain of about 10 dB at a BER of 10-5, at a cost of imposing a moderate throughput loss dedicated to a modest feedback overhead. Furthermore, our proposed ST-SSK scheme lends itself to efficient communication, because the deleterious effects of deep shadow fading no longer impose spatial correlation on the signals received by the antennas, which cannot be readily avoided by co-located antenna elements