## 2 Coexistence and Interference in WBASNs
### Inter-WBASN Coexistence and Interference  
In [8], experimentation is used to investigate the coexistence of WBASNs with regard to the inter-user interference effect. Degradation of performance in terms of packet delivery ratio and packet rate is clearly taken into account while varying the number of WBASNs and their transmission data rate. In the experiment, eight WBASNs were set up in which one consisted of a gateway and several nodes operating in the 2.4 GHz band. During the experiment, each WBASN sequentially switched on and transmitted until all WBASNs were transmitting simultaneously. The data rate of each WBASN was increased each  
Figure 1: Interference in WBASNs. minute until the maximum value was reached. The results of this experiment show that increasing the number of WBASNs adversely affects their packet delivery ratio (PDR) and packet rate. More specifically, at the maximum transmission rate, a large number of WBASNs joined to the network causes high degradation of PDR. When all WBASNs transmit simultaneously, increasing the data rate at each WBASN reduces the PDR. It is clear that an increase in the number of WBASNs and their transmission data rate will cause high performance degradation in WBASNs. Co-channel interference among nonoverlapping WBASNs is analyzed in [9]. The network topology was modeled in a two-dimensional geometric representation in which each WBASN transmission range was modeled as a unit disk graph. Further, the network topology includes one tagged WBASN and interfering WBASNs and was developed into an advanced geometrical probability function. Based on that model, a gamma distribution function was used to approximate the total interference in the WBASN. The impact of interference was analyzed in terms of the boundary network distance to preserve the acceptable SINR (signal to interference plus noise ratio). For example, the minimum network distance should be larger than 7 to 12.5 m to guarantee the SINR of the boundary nodes and at least 9 to 18 m to ensure the average SINR requirement of the WBASN. However, it is necessary to investigate the performance of the multiple access schemes for coexistence of WBASNs. In [10], the performance of three classic multiple access schemes is compared with respect to the probability of collision, the statistics of SINR, and bit error rate (BER). More specifically, the authors conducted the mathematical analysis to focus on: (1) the probability that one piconet collides with other piconets; and (2) the theoretical mean SINR for code division multiple access (CDMA), time division multiple access (TDMA), and frequency division multiple access (FDMA) schemes. The simulation results based on simultaneous measurement of signal and interference clearly show that TDMA is the best option in terms of BER and SINR in co-channel interference mitigation, and CDMA is not suitable. Otherwise, FDMA is the best solution for interference mitigation in uncoordinated WBASN networks. In [11], dynamic coexistence of IEEE 802.15.4-based WBASNs is investigated by using the theoretical analysis of successful transmission. The author analyzed the probability of successful beacon and data transmission of a WBASN in a dynamic hospital environment. The simulation shows that the number of lost beacons increases when the number of coexisting WBASNs changes. In the case of high-data-rate transmission, data loss is higher in the presence of interference. A mathematical model of interference among WBASNs in ISM (industrial, scientific, and medical) band is introduced in [12]. An experiment was set up in hospital, office, and home environments in Italy to measure the performance of WBASNs. The probability distribution function (PDF) of interference is defined based on those measurements. The maximum likelihood criteria are used to describe the PDF of the interference power. In [13], intra-WBASN and inter-WBASN interference is analyzed by considering the cognitive radio system-based WBASN (CR-WBASN). The CR-WBASN uses a simplified human body model consisting of six cylinders.