Analysis of the effectiveness of transmission power control as a location privacy technique

Abstract

Location privacy is an increasing source of concern for wireless users since their positions can be unwittingly estimated by malicious eavesdroppers. Transmission power control (TPC) is one of the various obfuscation techniques mentioned in the literature with the potential to provide location privacy to wireless users. This technique consists of letting the user vary the mobile node’s transmission power in a way that only the nearest eavesdropper can overhear the mobile node’s signals. This variation reduces the number of eavesdroppers overhearing the mobile node’s transmissions, thus increasing the location error estimated by nearby eavesdroppers, thereby improving the mobile user’s location privacy. Although some works have highlighted the advantages of TPC as a location privacy technique, no previous work has studied its effectiveness considering wireless channel impairments, hardware limitations, and localization algorithms used by eavesdroppers. This paper analyzes the real value of using TPC as a location privacy technique through a probabilistic model that measures the ability of TPC to effectively reduce the number of overhearing eavesdroppers. The results presented in this work show that the effectiveness of TPC is considerably affected by wireless channel impairments as well as by eavesdroppers’ density. Moreover, since off-the-shelf 802.11 radios have limited transmission power levels, real test-bed experiments showed that mobile users cannot always adjust their transmission power to fulfill the required levels of TPC. This is particularly the case in densely deployed scenarios in which most of the time the required transmission power is below the radio’s minimum transmission level. These results demonstrate the limited location privacy capabilities of TPC in most real-life scenarios, thus disproving previous claims that place TPC as a solution for the location privacy problem.