Abstract

Hidden nodes are a fundamental problem that can potentially affect any wireless network where nodes cannot hear each other. Although the hidden node problem is well known, so far only few papers have quantified its effects in a comprehensive manner. This paper represents a first step towards getting a quantitative insight into the impact of hidden nodes on the performance of wireless networks. We first carry out an exact queuing-theoretic analysis for a 4-node segment and derive analytical expressions for the probability of packet collision, the mean packet delay, and the maximum throughput, based on a model that closely follows the IEEE 802.11 standard. We then extend the analysis and provide an approximation for a general linear topology that is asymptotically exact at low load. Finally, we perform detailed simulations to validate our analytical results and show their applicability to predict the performance of IEEE 802.11 networks with hidden nodes. The simulation and analysis closely match. Moreover, they reveal that the impact of hidden nodes propagates through the network causing some nodes to saturate at load as low as 15% of the capacity.

Keywords: IEEE 802.11; Hidden nodes; Collision probability; Delay analysis; Maximum throughput analysis

Article Outline

1. Introduction

2. Background

2.1. Outline of the IEEE 802.11 basic access method

2.2. Related work

3. Model and simple analysis

3.1. The elementary topology

3.2. Statistical model

3.3. A simple ‘random-look’ analysis

4. Analysis and main results

4.1. Probability of packet collision in the elementary topology

4.2. Maximum throughput in the elementary topology

4.3. Mean packet delay in the elementary topology

4.4. Extension to general linear network

5. Proof of key expressions

5.1. Calculation of E[N|q_C(0)=0]

5.2. Calculation of E[N|q_C(0)>0]

5.3. Derivation of Pr{q_C(0)>0}

6. Simulation results

6.1. Validation of the analysis

6.2. Simulation of IEEE 802.11 network

6.2.1. Elementary topology

6.2.2. Linear topology

7. Conclusion

Acknowledgements

References