# Interference-Robust Transmission in Wireless Sensor Networks
## 1 Introduction
The collision-avoidance approach mainly exploits white space to avoid co-channel interference. A dynamic rate adaptation and control for energy reduction (DRACER) scheme adjusts the transmission rate in response to the change of operating condition [22]. DRACER may reduce the probability of collision with the interference signal by transmitting packets at the highest rate. However,  
Figure 1: signal-to-interference-plus-noise ratio (SINR) of IEEE 802.15.4 in the presence of co-channel interference. it does not consider the effect of the packet size in the presence of interference, yielding inefficient use of white space. A white space-aware frame adaptation (WISE) scheme considers the packet size control [15]. Modeling the idle period of interference as a Pareto-distributed random variable, WISE determines the packet size to maximize the throughput efficiency, while providing desired packet collision probability. However, it may need to periodically adjust the Pareto model through channel sensing, which may be a considerable overhead to low-power WSN devices. Another packet size control scheme, referred to as dynamic packet length control (DPLC), simply adjusts the packet size based on a transmission efficiency metric [23]. DPLC empirically determines the packet size after a number of packet transmissions. However, it may not properly work in the presence of time-varying interference. Moreover, these collision-avoidance schemes only consider the signal transmission at a fixed rate, which may not be efficient when the signal-to-noise ratio (SNR) is higher than that required for the rate. A payload size and transmission rate adjustment scheme was proposed for WLANs in slow fading channel environments [24]. However, it does not consider the presence of co-channel interference, making it impractical for application to low-power WSNs. As a collision-avoidance approach, partial packet recovery (PPR) techniques were proposed to reduce the transmission of acknowledgment (ACK) packets. They partition a data packet into a number of smaller blocks and acknowledge the transmission of multiple data packets by a single recovery frame including a block map, which describes the status of all blocks [25; 26; 27; 28]. The transmitter should retransmit all of the packets when the recovery frame is not received [25] or wait until it receives the recovery frame, while the receiver retransmits the recovery frame until it receives data packets [26; 27; 28]. The PPR techniques may severely suffer from frequent loss of recovery frames in practical operation environments. Moreover, they do not consider the waiting time when they evaluate the throughput and the energy consumption. The power consumption during the idle listening of WLAN and ZigBee devices is comparable to the power consumption during signal reception [29]. Moreover, these schemes only consider the transmission at a fixed rate. In this paper, we consider the adjustment of the transmission rate and payload size to improve the transmission performance in the presence of co-channel interference. We consider the operation of low-power WSNs that can support the bulk transfer of large data (e.g., e-price tags [30], surveillance applications involving imaging/acoustics [31; 32] and structural health monitoring [33; 34]). Based on the probability of transmission failure and the data throughput, we determine the payload size to maximize the data throughput in the presence of interference. It is shown that the transmission time maximizing the normalized throughput is little affected by the transmission rate, rather mostly by the interference condition. We independently adjust the transmission time and the transmission rate to maximize the data throughput in response to the change of operation environments. Finally, we evaluate the performance of the proposed scheme by computer simulation. The rest of this paper is organized as follows. Section 2 describes the WSN model in consideration. Section 3 analyzes the performance of WSN in the presence of co-channel interference.