Analyzing the Transitional Region in Low Power Wireless Links - Engineering Assignment Help

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Abstract—The wireless sensor networks community, has now an increased understanding of the need for realistic link layer models. Recent experimental studies have shown that real deployments have a “transitional region” with highly unreliable links, and that therefore the idealized perfect-reception-within-range models used in common network simulation tools can be very misleading. In this paper, we use mathematical techniques from communication theory to model and analyze low power wireless links. The primary contribution of this work is the identification of the causes of the transitional region, and a quantification of their influence. Specifically, we derive expressions for the packet reception rate as a function of distance, and for the width of the transitional region. These expressions incorporate important channel and radio parameters such as the path loss exponent and shadowing variance of the channel; and the modulation and encoding of the radio. A key finding is that for radios using narrow-band modulation, the transitional region is not an artifact of the radio non-ideality, as it would exist even with perfectthreshold receivers because of multi-path fading. However, we hypothesize that radios with mechanisms to combat multi-path effects, such as spread-spectrum and diversity techniques, can reduce the transitional region.

INTRODUCTION
Wireless sensor network protocols are often evaluated through simulations that make simplifying assumptions about the link layer, such as the binary perfect-reception-withinrange model. Several recent empirical studies [1] [2] [3] have questioned the validity of these assumptions. These studies have revealed the existence of three distinct reception regions in a wireless link: connected, transitional, and disconnected.
The transitional region is often quite significant in size, and is generally characterized by high-variance in reception rates and asymmetric connectivity. Particularly, in dense deployments such as those envisioned for sensor networks, a large number of the links in the network (even higher than 50%) can be unreliable due to the transitional region.

CONCLUSIONS AND FUTURE WORK
The impact that the channel behavior has on the performance of upper-layer protocols in wireless sensor networks requires a clear understanding of the different regions of low power wireless links. We have presented a detailed study of the transitional region. Some of the key contributions and conclusions of this work are:

-Mathematical link layer models are presented for the statistical variation of packet reception rates with respect to distance (for different environment and radio characteristics). This analysis yields the boundaries of the different regions — connected, transitional, and disconnected. The methodology presented can be easily extended to other radios that use different modulation and encoding schemes.

-The study shows the influence that the modulation, encoding, output power, frame size, noise floor, and channel parameters have on the transitional region.

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