New Switching Master/Slave Role Algorithm (SMSR)

c. Permutation reference positions algorithm of outdoors-SPs to mitigate the

impact of DOP issue. (as it is explained in the incoming subsection 5.4.1.3)

5. When an SPm is deep indoors and only 4 or less SPos are available in the BT

network, the SILS uses the WAPs as reference points to help locating this SPm. Pseudoranges between such SPm and WAPs are calculated by using time synchronised beacon signals in SP monitor mode. This location is now optimised with pseudoranges calculated with SPos.

5.4.1.1 Pseudorange Measurement via BT Signals

This subsection addresses the eighth research question (as it is listed in section 1.4): Can BT-Hop synchronisation between the connected SPs in a BT-network provides pseudorange measurements? To the best of my knowledge, the Hop-synchronisation counting would be the most accurate time measurement. This is concluded by after empirically experimenting with various methods to do the pseudorange measurements between two BT nodes. This is because, in a Piconet, when the connections between Master and Slaves have been made, both Master and Slaves generate a set of frequency sequences. This set of frequency sequences is called Hop-Sequences. These Hop- sequences’ values are generated by mixing of Master’s clock offset and MAC address. It means that Slaves can use the same Master’s clock to count the hop-frequencies and then synchronise with that clock [128].

Therefore, when a frame is being transmitted, both Master and Slaves should hop from one frequency to the next selected frequency at the same time. As illustrated in Figure 5-

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6, time stamping of the epochs of all frequency changes should be precise when an accurate source time (like GNSS receiver time) is used. The pseudorange measurement algorithm utilises modified POLL-NULL frames to calculate the TOF for every BT transmission. The master periodically broadcasts POLL frames to check the connectivity with its slaves and each connected slave responds the master by sending NULL frames [129].

In Figure 5-6, master generates T1 and T3 as timestamps (epochs) during sending POLL frames and receiving the NULL frames, respectively. To measure the TOF, T3 is subtracted by both T1 and Δt delay, where Δt delay is the static time processing delay of the received frame plus one slot time [129]. Then the pseudorange between the master and any slave is equal to the TOF multiplied by speed of light. The c-language code of this algorithm in the OPNET modeller is listed in Appendix B.1.

Figure ‎5-6: Pseudorange measurement using BT hop-synchronisation.

5.4.1.2 New Switching Master/Slave Role Algorithm (SMSR)

In the following steps, SILS applies a new SMSR algorithm between all SPs in the Piconet to reduce the error of all pseudoranges measurement. To achieve this

Start hop-sync counting or time / POLL packet transmission

time _{packet received}Time of NULL

T1and T3are based on

GNSS time (up to 6 nsec accuracy)

Time of NULL packet transmission

Pseudo-range= c * time_of_flight Where: c= speed of light

time_of_flight= T3-T1-∆tdelay

∆tdelayis a static delay of NULL packet

processing plus one slot (0.625 msec) Master

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improvement, SPm has to be the master of this Piconet and then generates a map of network location information. This map would be shared by all network SPs, for storing several measurements described in the following steps:

1. As a first step, SPm measures and stores its pseudoranges from all SPos in the

network based on the hop synchronisation counting. Later, it collects and stores all SPos GNSS positions on its memory (as shown in Figure 5-7). These position coordinates are appended into the “reserved bits” of the NULL frames that which are sent from the SPos to the SPm. Finally, it generates a list of master-slave switching sequence based on the measured BT-RSS values from all SPos. In most cases, this list guarantees that switching rotation will be based on nearest to furthest order.

Figure ‎5-7: Flow-chart of SMSR steps

2. The location map is then shared with all SPos and stored on SPs memory.

3. This step includes:

Note:

SPm: SP Master; SPos: SPs outdoors; PR: pseudorange

SPm measures & stores PRs from all SPos SPm collects and stores all SPos GNSS position SPm generates a list of master- slave switching sequence based

on the RSSI from all SPos The list master-slave switching

sequence shared with all SPos Master now surrenders his role to

the first SPo in the switching list

SPo Master measures, stores, and shares its PR from all SPs in the network SPo Master surrenders his role to the next SPo in the switching list

i <=No_SPos

This guarantees that the list will be nearest

to furthest order These positions are stored into the “reserved bits” of

the NULL packets Based on the hop synchronization counting

SPm becomes Slave and the SPo becomes

the new Master

SPo Master surrenders his role to SPm again SPm calculate its position using Linear LSF to enhance the SPm’s

own PR measurements

We can able to achieve a 50% improvement i=1

i=i+1

Least Square Fitting

No

Yes Start

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a. The SPm surrenders his role to the first SPo in the switching list. That is, the

SPm becomes slave and the SPo becomes the new master.

b. The new master measures and stores its pseudoranges from all SPs in the

network.

4. Again the new updated map of location information through the new SPo is shared

between all the SPs in the network

5. This SPo (within master role) will now surrender his role to the next SPo in the

switching list, and so on until the order reached the SPm again.

6. The SPm is now equipped with all the estimated pseudoranges from all switching

master-slave sequence list. This SPm calculate its position by using a LLS fitting technique to enhance the SPm’s own pseudoranges measurements. Through conducting many experiments via known SPs positions; the proposed SMSR algorithm is able to achieve a 50% improvement to the accuracy of the SPm position calculation.

A diagram of running SMSR algorithm on SPs is illustrated in Figure 5-8. SPm then performs the permutation algorithm described in next subsection to enhance its calculated position.

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Figure ‎5-8: BT switching master/slave role between connected SPs in a network.