# An Efficient Location Verification Scheme for Static Wireless Sensor Networks
## 7 Further Discussion  
The distance-inconsistency filtering is helpful to reduce the verification failure of the honest sensors, but it has a side-effect. A malicious sensor can pass the verification unintentionally because of the other malicious sensors. Figure 16 shows the example of the consideration. When the malicious sensor \(m\) is trying to fake its location at the position of \(m^{\prime}\), it needs the information from the MSR between \(v\) and \(m^{\prime}\). At this moment, a sensor \(z\) also reports the false location of itself as if it is at the position \(z^{\prime}\). Since the sensor \(z^{\prime}\) is located in the most critical position for the successful verification of the sensor \(m^{\prime}\), the information from the sensor \(z^{\prime}\) should be included in the calculation of _msrToken_. However, the information from sensor \(z^{\prime}\) will be excluded from the _msrToken_ calculation since the estimated distance \(d^{\prime}\) between sensor \(v\) and sensor \(z^{\prime}\) is different from the measured distance \(d\) between sensor \(v\) and sensor \(z\). Consequently, sensor \(m\) successfully passes the verification. However, the influence of the side-effect of the distance-inconsistency filtering is not huge under the moderate portion of malicious sensors, as shown in Section 6. This is because the design of the scheme is effective to suppress the impact of the side-effect when there are enough honest sensors in the network. Figure 16: The side-effect of the distance-inconsistency filtering. The next consideration is that the communication cost can be reduced more by using the piggybacking strategy. A verifier is able to send its location verification request in a piggybacked manner on the normal data packet, such as temperature data, to initiate the process. Thus, a claimant needs to send only one packet to finish the location verification process. Note that sensors cannot delay their response until the data packet is generated due to the collaboration attack case. In this case, the number of packets required can be decreased from two to one per verifier. Consequently, it would be possible to reduce the overall communication cost with this approach. Third, the frequency of the location verification may be an important factor for the time-critical applications. The verification result can be cached for a certain period of time to reduce the verification overhead in the applications. However, it should be carefully designed because the prolonged validity of the verification result may give the adversaries a chance to bypass the verification process. The fourth consideration is the vague communication range in the real world. Since the communication range is unclear in the real world, there is a chance that some neighbors receiving location verification requests with a weak signal power do not react to the location verification procedure correctly and degrade the performance of the scheme. This problem can be resolved by defining and using the range for the verification that is different from communication range. However, the difference of the verification range at each sensor will cause the malfunction of the verification. This makes the range fixed all of the time. In addition, the determination of the proper range would be a difficult problem. If the range is getting smaller, the area of EMSR becomes smaller, as well. This will cause a high probability of no sensor being in the EMSR, and it consequently leads to more occurrences of the false acceptance of malicious sensors. Thus, the range should be determined very carefully. Finally, the mobility of sensors can be considered to widen the application of the proposed scheme. Basically, the proposed verification is designed for a static wireless sensor network. The mobility of any sensor will have the same effect as the malicious sensor. As a consequence, the honest sensors with mobility will experience false rejection, while the malicious ones will be successfully rejected in most cases.