# RSS Indoor Localization Based on a Single Access Point
## 3 Proposed Approach  
### High-Level Description of the Proposed Approach  
In this paper, we present a new localization approach based on a single, multi-antenna AP, where each AP antenna acts as a separate transmitter. By carefully configuring the orientation and polarization of each antenna, one can influence the RSS values that form the fingerprint radiomap. RSS from different antennas can then be combined in order to generate a _multi-layer radiomap_. The multi-layer radiomap is defined as the unified data set created, from the fusion of RSS and antenna identification data recorded at each receiver location. In order to practically achieve such a task, the APs' wireless drivers should be capable of supporting _Radiotap_, which is a de facto standard for 802.11 frame injection and reception. _Radiotap_ offers the capability to retrieve additional information about 802.11 frames, from the driver to userspace applications, and defines two important antenna fields: Firstly, the _IEEE80211_RADIOTAP_ANTENNA_ field, a unit-less indication of the Rx/Tx physical antenna identification (Antenna ID), which is a parameter important for identifying the exact transmitting source of the RSS recorded by the Mobile User (MS); and secondly, the _IEEE80211_RADIOTAP_DBM_TX_POWER_ field, which provides the RF signal power. A typical code snippet of transmission definitions for the Atheros driver is presented below:  
```
#defineATH_TX_RADIOTAP_PRESENT( \ \ \\ (1 << IEEE80211_RADIOTAP_TSFT)|\ \ \\ (1 << IEEE80211_RADIOTAP_FLAGS)|\ \ \\ (1 << IEEE80211_RADIOTAP_RATE)|\ \ \\ (1 << IEEE80211_RADIOTAP_ANTENNA)|\ \ \\ (1 << IEEE80211_RADIOTAP_DBM_TX_POWER)|\ \ \\ (1 << IEEE80211_RADIOTAP_XCHANNEL)|\ \ \\ 0) structath_tx_radiotap_header{ structieee80211_radiotap_headerwt_ihdr; uint64_twt_tsf; uint8_twt_flags; uint8_twt_rate; uint8_twt_antenna; uint8_twt_txpower; uint32_twt_chan_flags; uint16_twt_chan_freq; uint8_twt_chan_ieee; int8_twt_chan_maxpow;
```  
As mentioned earlier, each combination of different antenna orientations will potentially generate a different candidate radiomap. For example, in the case of a single AP with two dipole antennas, a Scenario could include both antennas to be set in the vertical-z axis direction. Another Scenario may assume that the first antenna is kept at the vertical orientation, while the second antenna is at a horizontal orientation pointing at zero degrees. A different Scenario may maintain the first antenna at the vertical orientation, and the second antenna to be reconfigured at 45 degrees or 90 degrees at the horizontal level, and so forth. Scenarios may also assume different antenna orientations at the receiver site. The aforementioned typical Scenarios are illustrated in Figures 1 and 2. After preparing the desired Scenarios, simulations were run in order to generate the respective radiomaps. Each radiomap was evaluated through various localization algorithms, noting the resulting positioning error. Based on the results, the best performing radiomap was finally selected to be implemented in the RSS-based fingerprint localization platform. For the purposes of our experiment, we utilized TruNET wireless, a deterministic radio planning simulator. Initially, the area of interest was designed in a _TruNET wireless_ simulator, taking into consideration the different building structure geometries, dimensions, and material constitutive parameters. A list of different Scenarios was also created by configuring the wireless network antennas, as described previously. The wireless network consisted of a single Access Point (AP) with a minimum of two monopole antennas. The proposed approach is applicable to any antenna type. Afterwards, a simulation took place for each Scenario, and a candidate multi-layer radiomap was generated based on the fused antenna information. More specifically, each AP antenna was considered as a separate transmitter. The calculated RSS values, linked with the transmitting source (Antenna ID), were registered in the receiver cells.