Probability of error for noncoherent M-ary orthogonal FSK with postdetection switched combining

The paper extends the notion of postdetection switched combining introduced by the authors to M-ary orthogonal modulation (Alouini and Simon, ibid., p.1591-1602, 2003) and proceeds to analyze and evaluate its average bit-error rate performance for the dual-branch case. The particular variation chosen for the switching strategy uses a different model than that previously used for the binary case and although it results in a slightly poorer performance, it nevertheless outperforms conventional (predetection) switched combining for all values of M. Results are obtained for a variety of popular channel models including Rayleigh, Rician, and Nakagami-m fading. Because of its relative simplicity of implementation, the proposed scheme once again offers a very attractive low-complexity solution for mitigating the deleterious effects of multipath fading.     

A unified approach to the probability of error for noncoherent anddifferentially coherent modulations over generalized fadingchannels

We present a unified approach to determine the exact bit error rate (BER) of noncoherent and differentially coherent modulations with single and multichannel reception over additive white Gaussian noise and generalized fading channels. The multichannel reception results assume independent fading in the channels and are applicable to systems that employ post-detection equal gain combining. Our approach relies on an alternate form of the Marcum Q-function and leads to expressions of the BER involving a single finite-range integral which can be readily evaluated numerically. Aside from unifying the past results, the new approach also allows for a more general solution to the problem in that it includes many situations that in the past defied a simple solution. The best example of this occurs for multichannel reception where the fading on each channel need not be identically distributed nor even distributed according to the same family of distributions     

Channel characterization and modeling for Ka-band very smallaperture terminals

An increasing number of commercial applications are being promoted for future Ka-band satellite communication systems. Many of these systems will involve low-margin very small aperture terminals (VSATs). These systems are subject to important atmospheric propagation degradations that affect the quality of transmission and the link availability. The objective of this paper is to characterize the Ka-band channel and evaluate the performance degradation in VSATs resulting from atmospheric propagation, impairments. In particular microwave propagation through a turbulent atmosphere is discussed, and the statistical characterization and modeling of tropospheric scintillation is reviewed. Moreover, the paper extends the method proposed by Filip and Vilar (1990) for the long-term characterization and modeling of the combined effect of rain impairments and scintillation. Specifically, the increase in noise temperature during rain events is added to the Filip-Vilar model. This leads to a five-parameter global fading distribution that is used to predict typical Ka-band satellite link outage time, the mathematical formalism is illustrated by applying the method to the selected case of the Advanced Communications Technology Satellite (ACTS)-Georgia Tech experimental downlink. Numerical results confirm that both rain impairments and scintillation are important factors in the design of Ka-band VSAT systems     

Postdetection switched combining - a simple diversity scheme with improved BER performance

This paper develops, analyzes, and optimizes a simpler form of dual-branch switch-and-stay combining (SSC), namely, one that relies on the output signal plus noise rather than the instantaneous signal-to-noise ratio (SNR) to trigger the switching between the diversity branches. Analysis supported by numerical results show that the newly proposed postdetection SSC scheme outperforms predetection SSC and this performance gain increases as the channel conditions improve in terms of average SNR and/or severity of fading. In brief, when simplicity of implementation is of primary concern, as is the case, for example, in mobile units, the proposed scheme offers an attractive low-complexity solution to mitigate the deleterious effects of multipath fading.     

Performance comparison of different selection combining algorithms in presence of co-channel interference

In this paper, we present a unified approach for the computation of the outage probability, the level crossing rate (LCR), and the average outage duration (AOD) of selection combining (SC) in the presence of multiple cochannel interferences and under both minimum signal-to-interference ratio (SIR) and desired signal power constraints. We consider three selection algorithms, namely: 1) the best signal power algorithm; 2) the best SIR algorithm; and 3) the best total power (desired plus interference) algorithm. As a specific application example, we analyze the three algorithms for a low-complexity dual-branch SC receiver subject to multiple interferers over Rayleigh fading channels. When applicable, the new results are compared to those previously reported in the literature dealing with the outage probability, AOD, and LCR of 1) interference-limited systems and 2) power-limited systems. Numerical examples show that the minimum desired signal power constraint induces a floor to the outage probability, AOD, and LCR performance measures. They also show that the best SIR algorithm provides the best outage probability and AOD performance for low average SIR. On the other hand, the best signal power algorithm and the best S+I algorithm outperform the best SIR algorithm for high average SIR. It is also shown that the best SIR algorithm tends to have more outage level crossings.     

Performance Analysis of Joint Adaptive Modulation and Diversity Combining Over Fading Channels

Both adaptive modulation and diversity combining represent important enabling techniques for future generations of wireless communication systems. In this paper, capitalizing on recent developments in adaptive combining, we propose three joint adaptive modulation and diversity combining (AMDC) schemes. With these schemes, the modulation mode and diversity combiner structure are adaptively determined based on the fading channel condition and error-rate requirement. We accurately analyze these three AMDC schemes in terms of processing power consumption, spectral efficiency, and error-rate performance. Selected numerical examples show that the proposed AMDC systems meet the target error-rate requirement while achieving high spectral efficiency with low processing power consumption     

Soft handover overhead reduction by RAKE reception with finger reassignment

We propose and analyze in this paper a new finger assignment technique that is applicable for RAKE receivers when they operate in the soft handover (SHO) region. This scheme employs a new version of generalized selection combining (GSC). More specifically, in the SHO region, the receiver uses by default only the strongest paths from the serving base station (BS) and only when the combined signal-to-noise ratio (SNR) falls below a certain pre-determined threshold, the receiver uses more resolvable paths from the target BS to improve the performance. Hence, relying on some recent results on order statistics we attack the statistics of two correlated GSC stages and provide the approximate but accurate closed-form expressions for the statistics of the output SNR. By investigating the tradeoff among the error performance, the path estimation load, and the SHO overhead, we show through numerical examples that the new scheme offers commensurate performance in comparison with more complicated GSC-based diversity systems while requiring a smaller estimation load and SHO overhead.     

Estimation of Nakagami-m fading channel parameters with application to optimized transmitter diversity systems

An optimum power loading algorithm for transmitter diversity systems over correlated and unbalanced Nakagami (1960) paths and its performance evaluation under perfect channel estimate conditions are derived. In addition, various online estimators of the required Nakagami channel parameters for optimized power loading and the comparison of their mean square error via Monte Carlo simulations are presented. Some of these estimators are used to obtain the performance of optimized transmitter diversity systems under imperfect channel estimation (ICE). These numerical results show that the diversity gain of these optimized systems compared with equipower systems increases as the severity of fading decreases and as the degree of branch imbalance increases even under ICE. On the other hand, in weakly correlated and (or) unbalanced branches, optimized transmitter diversity systems offer negligible gain or even losses compared with unoptimized systems because of the ICE.     

Effect of imperfect phase and timing synchronization on the bit-error rate performance of PSK modulations

A great deal of attention has been devoted in the recent literature to the study of the bit-error rate (BER) performance of phase-shift keyed (PSK) constellations, due to their high spectral efficiency. It is well known that an error in phase or timing synchronization affects the probability of correct decisions at the receiver. This problem becomes much more significant as data rates increase, and the corresponding symbol durations decrease. In this letter, we look into this problem and analyze the exact BER performance of generalized hierarchical PSK constellations under imperfect phase or timing synchronization over additive white Gaussian noise channels.