Number Of Diversity Paths Research Articles

A Simple Technique to Enhance Diversity Order in Wireless Fading Relay Channels

Relaying has proven to be an effective method of providing additional spatial diversity on wireless fading channels. This paper proposes a system of XORing at the relay with iterative maximum a posteriori (MAP) decoding at the destination. An XOR-relay offers an increased number of diversity paths, enabling the destination to construct a cycle- free decoding structure, and resulting in an enhanced diversity order. Simulation results clearly show that the proposed scheme approaches 3rd-order diversity in the topology of second diversity paths, with no need for additional resources.

Channel Quality Estimation Index (CQEI): A Long-Term Performance Metric for Fading Channels and an Application in EGC Receivers

We introduce the channel quality estimation index (CQEI) as an alternative improved long-term performance criterion for wireless communications systems operating over fading channels. CQEI is simple to evaluate, since it depends on the channel statistics which vary much more slowly than the channel state itself, and thus can be obtained at the initialization state using a long training sequence and afterwards continuously improved during the whole communication period. Considering generalized fading channels (Nakagami-m, Nakagami-n, Nakagami-q) and a variety of modulations, we show that CQEI assesses the average error performance of a communication system more efficiently, compared to other long- term performance criteria such as the average signal to noise ratio (ASNR) and the amount of fading (AoF). As an application, we utilize CQEI to present a new class of equal gain combining (EGC) receivers operating over non-identical independent fading channels, called selection-EGC (S-EGC). This kind of receivers reduces or eliminates the combining loss by rejecting the weak branches that contribute more to increasing the noise than the signal during the combining stage. S-EGC could be efficiently applied in the emerging broadband communication systems (e.g., ultra-wideband), where the number of diversity paths can be considerably large due to the strong multipath effects. Numerical results show that the new proposed selection-EGC (S-EGC) receiver outperforms the classical one, when fading with non- identically distributed diversity branches is assumed.

Generalized Switch-and-Examine Combining (GSEC): A Low-Complexity Combining Scheme for Diversity-Rich Environments

In diversity-rich environments, there is a tradeoff between performance and complexity. While combining a large number of diversity paths improves the system performance, it also increases the receiver complexity. With this in mind, we propose generalized switch and examine combining (GSEC) as a good candidate combining scheme for such environments. Description of the GSEC mode of operation shows that this scheme conserves a fixed complexity as the number of diversity paths increases, and offers a considerable complexity savings over traditional maximum ratio combining and even other low-complexity schemes, such as generalized selection combining. In this paper, we look into the design and performance analysis of GSEC over independent and identically distributed diversity paths. As an illustration of the mathematical formalism, selected numerical examples are provided, together with some related discussions and interpretations.