Serdar Ozyurt

Exact Joint Distribution Analysis of Zero-Forcing V-BLAST Gains with Greedy Ordering

We derive the joint probability distribution of zero-forcing (ZF) V-BLAST gains under a greedy selection of decoding order and no error propagation. Unlike the previous approximated analyses, a mathematical framework is built by applying order statistics rules and an exact closed-form joint probability density function expression for squared layer gains is obtained. Our analysis relies on the fact that all orderings are equiprobable under independent and identical Rayleigh fading. Based on this idea, we determine the joint distribution of the ordered gains from the joint distribution of the unordered gains. Our results are applicable for any number of transmit and receive antennas. Although we present our analysis in a ZF V-BLAST setting, our analytical results can be directly applied for the dual cases of ZF V-BLAST. Under the assumption of a low rate feedback of decoding order to the transmitter, a benefit of having exact expressions is illustrated by the calculation of the cutoff value under optimal power allocation that maximizes the sum of the substream outage capacities under a given sum power constraint. We provide numerical results and verify our analysis by means of simulations.

An exact outage analysis of zero-forcing V-BLAST with greedy ordering

In this paper, an outage probability analysis is carried out on zero-forcing (ZF) vertical Bell Labs Layered Space-Time (V-BLAST) algorithm based on a greedy selection of decoding order, which is optimal in diversity-multiplexing tradeoff sense. We provide a mathematical framework to make the analysis tractable and derive the probability density function expressions of the squared substream gains. Especially, we obtain a compact expression on the joint pdf of squared substream gains for any number of transmit and receive antennas. Moreover, using the analytical results, we illustrate the optimum cutoff value under optimal power allocation that minimizes the total consumed power for a given target total rate. Finally, we provide numerical results and verify our analysis by means of simulations.

Performance analysis of maximal ratio combining with transmit antenna selection and signal space diversity under exponential antenna correlation

In this work, signal space diversity (SSD) is incorporated into a multiple-input multiple-output system with maximal ratio combining and transmit antenna selection. The performance of the proposed system with phase-shift keying (PSK) modulation is studied under a slow flat Rayleigh fading channel scenario with the correlated receive antennas. By adopting the realistic exponential correlation model, an exact closed-form expression is derived for pairwise error probability. The optimal rotation angles are obtained for binary and quadrature PSK signal constellations. The theoretical analysis is verified by the numerical simulations. It is shown that the error performance of the system can be improved with almost no extra complexity or cost. It is also demonstrated that the proposed scheme with SSD is more resistant against the studied correlation model as compared to the original scheme without SSD.

Performance of rotated phase shift keying modulation over Ricean fading channels

The performance of PSK modulation over fading channels can be improved by resorting diversity techniques such as space, time, frequency, and modulation diversity. In this paper, the modulation diversity is used to improve the performance of PSK modulation over fading channels, modulation diversity can be achieved by rotating the signal constellation and using component interleaving. We show that rotated signal constellations with the component interleaving improve the performance of M-PSK modulation (M=2,4,8) significantly as compared to the unrotated ones over Ricean fading channels. For example, when the ratio of the direct path lower to the multipath signal power, K is 0 and 10, 9 dB and 2 dB gains are obtained respectively at a symbol error probability of 10/sup -3/ for 8PSK modulation. We also show that as K gets larger, the gain obtained by the rotation rapidly decreases.

Design of frequency upconversion and downconversion blocks for 240 GHz communication systems

In this study, a communication system with 10 Gbps data rate is designed and its performance is investigated by using OOK (On-Off Keying) modulation in the 240 GHz band. OOK Modulation is carried out in a relatively low frequency band and is transported to the targeted high frequency band. The frequency downconversion is achieved by multiplying the generated local oscillator signal by the carrier signal from the communication channel. The downconverted signal is demodulated and the recovered signal is observed.

Performance analysis of signal space diversity with transmit antenna selection and maximal ratio combining

A multiple input multiple output communication system with transmit antenna selection and maximal ratio combining is combined with signal space diversity and its performance is investigated by means of statistical methods. To this end, signal constellation rotation angles minimizing error probability are obtained for phase shift keying modulation under Rayleigh fading channel when the modulation level is two and four. The positive effect of proper rotation angles on the system error performance is illustrated.

Outage and Diversity Analysis of Opportunistic Beamforming over Rayleigh Channels

In a multiuser system, the multiuser diversity gain capitalizes primarily on the dynamic range of channel fluctuations. When the channel varies slowly, opportunistic beamforming using multiple antennas at the transmitter can be used to generate artificial temporal fading resulting in amplified multiuser diversity gain [1]. When there exists a sufficient number of users in the system, opportunistic beamforming has been shown to achieve similar throughput as true beamforming but with much more limited feedback [2]. In particular, it has been shown that the required number of users to achieve near true beamforming throughput on the number of transmit antennas is exponential when each user is equipped with single antenna [2]. In this paper, a framework is presented to analyze the outage probability, diversity order and array gain of opportunistic beamforming over Rayleigh fading channels. First, we obtain an exact closed-form expression for the outage probability. Then, using some approximations, we show that the number of users must be at least the same as the number of transmit antennas in order to achieve full diversity. We quantify the array gain for the full diversity case and establish the dependence of the array gain on the number of users. Finally, we verify our analysis with numerical results.

Performance of phase shift keying modulation with rotated signal constellation over Ricean fading channels

Özet Bu çalışmada, işaret diyagramını uygun bir şekilde döndürerek ve bileşen serpiştirici/geri-serpiştirici kullanarak faz kaydırmalı anahtarlama (FKA) modülasyonunun sönümlemeli kanallardaki başarımının arttırılabileceği gösterilmektedir. Ele alınan teknik ile, Ricean sönümlemeli kanal üzerinde (doğrudan alınan işaretin gücünün saçılmış işaretin gücüne oranı, K=10 için) 8-FKA modülasyonunda 10 sembol hata olasılığı için yaklaşık 2 dB kazanç sağlanmaktadır.