VOL. 11, NO. 24, DECEMBER 2016 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences © 2006-2016 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 14497 A CROSS-LAYER APPROACH IN SUPPORT OF REAL-TIME DATA OVER WIRELESS SENSOR NETWORKS Albeiro Cortés Cabezas Department of Electronic Engineering, Surcolombiana University, Grupo de Tratamiento de Señales y Telecomunicaciones, Pastrana Av. Neiva Colombia E-Mail: albecor@usco.edu.co ABSTRACT It is widely known that energy efficiency is very important in wireless sensor networks (WSN). As a result, a common protocol design guideline has been to trade off some performance metrics such as throughput and delay for energy, which also goes well in line with many WSN applications. However, there are other applications with real-time constraints, such as those involved in surveillance or control loops, for which WSN still need to be energy efficient but also need to provide better performance, particularly latency and jitter. This article presents LEMR, a cross-layer design-based communication stack that not only preserves the energy efficiency of current alternatives but also coordinates the transfer of packets from source to destination in such a way that latency and jitter are improved considerably. Coordination is based on hop-distance to the sink, a new MAC layer, and physical layer information. Our approach adopts the Clear Channel Assessment (CCA) and Low Power Listening (LPL) strategies along with channel polling, which is a proven energy-saving method involving the physical and MAC layers. Simulation experiments demonstrate the superiority of LERM in terms of latency and jitter and energy when compared with well-known protocols, such as TMAC, S-MAC and SCP-MAC Keywords: wireless, sensor, network, MAC, routing, energy, latency. 1. INTRODUCTION Rapid advances in micro-electro-mechanical systems (MEMS) and low power digital electronics have made possible the development of wireless sensor networks (WSN). A WSN typically comprises of small wireless devices deployed over the physical environment, which cooperate in sensing, processing and communication tasks to provide data about the variables of interest for monitoring and decision making purposes. There are many WSN monitoring applications developed so far in the areas of security, environmental applications, transportation, home automation, civil engineering, etc. It is well known that wireless sensor devices are very limited in terms of communication and processing capabilities, and storage and energy resources, and that energy is of prime importance. As a result, most algorithms and protocol designs have been made energy efficient. Further, given the characteristics of typical monitoring applications for WSN, a common design practice has been to save energy at the expense of more relaxed QoS performance guarantees, such as low cannel utilization, and longer delays and jitter. For example an approach often used for saving energy has been to design MAC protocols that turn the radios off as much as possible. While this practice saves precious energy, it does it at the expense of worse latency and throughput. Therefore, most of these energy efficient protocols limit the use of WSN to those applications where a prompt response, a delay bounded message delivery, is not important. While this may be a good practice for many applications, there are some applications, such as surveillance and real-time control systems, for which WSN not only need to continue to be energy efficient but also provide better performance. In this paper we propose LERM (Latency, Energy, MAC and Routing) to fill this gap. LERM is a cross-layer design protocol for wireless sensor networks involving the physical, data link, and network layers of the communication protocol stack. LERM uses physical layer information to improve the reliability in packet transmissions. It includes a new medium access control layer for low energy consumption, and a new node coordination function for low latency and jitter packet forwarding. Through extensive simulation experiments we show the superiority of the LEMR protocol in terms of energy consumption, latency and jitter compared with S- MAC, TMAC and SCPMAC, three well-known energy- efficient MAC layer protocols. The rest of the paper is organized as follows. Section 2 lists the most important causes of energy wastage in WSN. Section 3 includes a brief related work on cross-layer design approaches and medium access control protocols. Section 4 describes the LEMR protocol. Section 5 presents a performance analysis. Section 6 presents the results of the performance evaluation. Finally, Section 7 concludes the paper. 2. ENERGY AND PERFORMANCE-RELATED ISSUES IN WSN In this section, a list of the most important issues related to energy consumption, latency and jitter in WSN are included, mostly from the MAC layer point of view. These issues, which should guide the design of algorithms and protocols for WSN according to the application needs, are the following:  Collisions: Collisions should be avoided because the extra energy wasted in frame retransmissions. Recall that communication is the most energy spending function in WSN. Collisions need to be avoided because they also affect the average latency and jitter.