This paper investigates packet delivery performance in dense wireless sensor networks, focusing on three environments: an indoor office building, a habitat with moderate foliage, and an open parking lot. The authors use a systematic approach to measure packet delivery performance, considering both the physical layer and the medium-access layer. Key findings include: 1. **Environmental Impact**: Packet loss rates vary significantly across different environments, with the indoor office building showing the highest packet loss rates. 2. **Physical Layer Coding**: Different physical layer coding schemes (4b6b, Manchester, and SECDED) affect packet delivery performance, with SECDED performing better due to its error correction capabilities. 3. **Transmit Power**: Lower transmit powers generally improve packet delivery performance, as they reduce the spatial extent of communication and thus the likelihood of multi-path interference. 4. **Gray Area**: A significant "gray area" exists within the communication range of nodes, where packet reception is highly variable and often poor. 5. **Signal Strength**: Received signal strength can provide some indication of link quality, but it is not a perfect predictor of packet loss. 6. **Spatial Correlation**: Packet loss among receivers is moderately correlated, with higher correlation in the open parking lot environment compared to the indoor office building and habitat. 7. **Temporal Variability**: Packet loss rates can vary significantly over time, with receivers near the edge of the communication range experiencing higher variability. The authors suggest that topology control mechanisms, which carefully select neighbors based on measured packet delivery performance, could improve network efficiency and reliability in harsh environments.This paper investigates packet delivery performance in dense wireless sensor networks, focusing on three environments: an indoor office building, a habitat with moderate foliage, and an open parking lot. The authors use a systematic approach to measure packet delivery performance, considering both the physical layer and the medium-access layer. Key findings include: 1. **Environmental Impact**: Packet loss rates vary significantly across different environments, with the indoor office building showing the highest packet loss rates. 2. **Physical Layer Coding**: Different physical layer coding schemes (4b6b, Manchester, and SECDED) affect packet delivery performance, with SECDED performing better due to its error correction capabilities. 3. **Transmit Power**: Lower transmit powers generally improve packet delivery performance, as they reduce the spatial extent of communication and thus the likelihood of multi-path interference. 4. **Gray Area**: A significant "gray area" exists within the communication range of nodes, where packet reception is highly variable and often poor. 5. **Signal Strength**: Received signal strength can provide some indication of link quality, but it is not a perfect predictor of packet loss. 6. **Spatial Correlation**: Packet loss among receivers is moderately correlated, with higher correlation in the open parking lot environment compared to the indoor office building and habitat. 7. **Temporal Variability**: Packet loss rates can vary significantly over time, with receivers near the edge of the communication range experiencing higher variability. The authors suggest that topology control mechanisms, which carefully select neighbors based on measured packet delivery performance, could improve network efficiency and reliability in harsh environments.