SUMMARY Cooperative diversity systems have recently been proposed as a way to form virtual antenna schemes without utilizing collocated multiple antennas. In this paper, we consider the Nth best opportunistic amplify‐and‐forward (AF) cooperative diversity systems. The AF type can be regarded as one on the basis of modified channel state information. Wireless channels between any pair of nodes (i.e., direct and dual hop links) are assumed quasi‐static independent and nonidentically distributed (INID) Rayleigh fading. The best opportunistic AF (OAF) scheme requires two phases of transmission. During the first phase, the source node transmits a signal to all relays and the destination. In the second phase, the best relay is only selected on the basis of highest signal‐to‐noise ratio (SNR) scheme to forward the source signal to the destination. Therefore, the indirect link (i.e., source‐selected relay destination) can give the highest received SNR. However, the best relay selection cannot be available so that we might choose the second, third, or generally the Nth best relay. In this paper, we derive the approximated outage probability and channel capacity for the Nth best OAF relay systems over INID Rayleigh fading channels. At first, the indirect link's received SNR is approximated as harmonic mean upper bound. With this information, we obtain the given relay's Nth best selection probability as the closed form. Finally, both outage probability and channel capacity are derived as the closed forms. Simulation results are finally presented to validate the analysis. Copyright © 2011 John Wiley & Sons, Ltd.

SUMMARYIn this paper, we derive another exact average error rate expression for the Nth best decode‐and‐forward relay systems over Rayleigh fading channels. On the basis of error‐events at relay nodes, the Nth best relay's selection probability is expressed as a more tractable form in which the number of summations and the length of each summation are specified. Then, exact average error performance metrics are obtained as two well‐known forms. The first is expressed with a moment generating function, and the other is presented as a closed form. Simulation results are finally presented to validate that the derived analytical expression can be a general frame work covering all Rayleigh fading channel conditions. Copyright © 2012 John Wiley & Sons, Ltd.

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This paper presents a performance analysis of dynamic channel allocation (DCA) based on the greedy approach (GA) for orthogonal frequency-division multiple access downlink systems over Rayleigh fading channels. The GA-based DCA achieves its performance improvement using multiuser diversity. We analyze the statistics of the number of allocable users that represents the multiuser diversity order at each allocation process. The derived statistics are then used to analyze the performance of GA-based DCA. The analysis results show that the number of subcarriers allocated to each user must be equal to achieve the maximum system performance based on outage probability and data throughput. cellular systems, the average channel gain of each user has a different value depended on the large-scale fading such as path loss. However, the effect of large-scale fading is reflected in the bandwidth assignment of each user, s m . So, this assumption is feasible for the channel allocation process.

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SUMMARYThis paper presents an analysis of asynchronous multicarrier-code division multiple access (MC-CDMA) systems over frequency-selective multipath fading channels when the carrier frequency offsets (CFOs) of all users are random variables and the frequency offset for the desired user is compensated. The effect of residual CFO on the average bit error rate (BER) is evaluated by the semi-analytical method, then the approximated BER performance is obtained as a closed-form expression. Moreover, the signal-tonoise ratio (SNR) loss caused by residual CFO is evaluated. Derived results show that the performance degradation due to residual frequency offset is negligible if the estimation error of CFO for the desired user is less than the normalized value of 10 −1 .

Motivated by the difficulty in measuring channel state information between heterogeneous primary and secondary systems, we propose a signal-to-interference-noise ratio (SINR)-based spectrum sharing policy. In the proposed spectrum sharing policy, a secondary user who does not cause SINR outage at the primary receiver is admitted to share the primary user's spectrum. In this article, we analyze the achievable rate of a secondary user and for whom the achievable rate is maximized in the SINR-constrained spectrum sharing. The maximized achievable rate is determined by the ratio of the distance between the secondary transmitter and the primary receiver to the distance between the secondary transmitter and receiver, and it is proportional to the distance ratio. In conclusion, secondary links with large distance ratio can support high data rate applications so long as SINR constraint of the primary user is guaranteed. 2012; 25:404-13 ‡ Two consecutive SINR measurements are performed in a coherence time. For example, assuming the carrier frequency is 2 GHz, the coherence times are about 15 and 10 ms for the velocity 10 and 15 m/s, respectively.

This paper presents an exact average symbol error rate (ASER) for the Nth best opportunistic (NO) one-way amplify-and-forward (OWAF) relay networks with M-phase shift keying (M-PSK) transmission over Rayleigh fading channels. This analysis begins with the max · min relay link selection (RLS) algorithm by using full channel state information (FCSI) for NO-OWAF networks and the given relay's selection probability is derived. Then, the modified moment generating function (MGF) is exactly presented with regard to the Nth best relay's selection probability. Based on the modified MGF, the exact ASER expression is shown as a form with the specified the number of multiple summations and the specified length of each summation. Furthermore, the accuracy of derived ASER performance is verified by simulation results.