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In this paper, the modulation diversity is used to improve the performance of M-PSK modulation over fading channels. Modulation diversity can be achieved by rotating the signal constellation and using component interleaving. We derive symbol error probability expressions for rotated uncoded M-PSK over Ricean fading channels and obtain optimal rotation angles for M-PSK (M = 2, 4, 8). We show that rotated signal constellations with component interleaving improve the performance of M-PSK significantly as compared to the unrotated one over Rayleigh and Ricean fading channels. For example, when the ratio of the direct path power to the multipath signal power, K is 0 and 10, 8 and 1.5 dB gains are obtained, respectively, at a symbol error probability of 10 −3 for 8PSK modulation. We also show that as K gets larger, the gain obtained by the rotation rapidly decreases. We develop a new asymmetric 8PSK signal constellation obtained from two QPSK signal constellations that are optimally rotated by different angles. This asymmetric 8PSK and also the rotated 8PSK signal constellation together with component interleaving are applied to four-state trellis-coded schemes. Simulation results show that these new schemes provide good performance improvements over the original TCM schemes and previous relevant works over Rayleigh and Ricean fading channels.

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Abstract-In this letter, an exact performance analysis is presented on the sum rate of zero-forcing beamforming with a greedy user scheduling algorithm in a downlink system. Adopting water-filling power allocation, we derive a compact form for the joint probability density function of the scheduled users' squared subchannel gains when a transmitter with multiple antennas sends information to at most two scheduled users with each having a single antenna. The analysis is verified by numerical results.Index Terms-Zero-forcing beamforming, water-filling power allocation, user scheduling, sum rate.

The forthcoming communications standards are conjectured to require unprecedentedly high spectral efficiency values. Motivated by this fact, we propose a new transmission scheme for multiple-input multiple-output systems, which is termed as power permutation modulation (PPM). In addition to the conventional data-carrying modulated symbols, some amount of extra information is conveyed in the distinct permutations of power allocation levels associated with the modulated symbols. The detection of the additional bits is performed by a power permutation recovery process at the receive side. Unlike the common approach, the power allocation is exploited as a new degree of freedom for carrying information without requiring any channel state information at the transmitter. The application of the introduced method is exemplified for zero-forcing beamforming and space-time block coding systems under digital phase modulation. It is shown that, without any important additional complexity, some notable signal-to-noise ratio gains (as large as 3 dB) are attained as compared to the standard approaches. An exact closed-form result on the bit error rate (BER) of the presented PPM scheme is provided. The obtained expression is used to obtain the optimum power allocation levels such that the overall BER is minimized.