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When multiple Wireless Body Area Networks (WBANs) are aggregated, the overlapping region of their communications will result in internetwork interference, which could impose severe impacts on the reliability of WBAN performance. Therefore, how to mitigate the internetwork interference becomes the key problem to be solved urgently in practical applications of WBAN. However, most of the current researches on internetwork interference focus on traditional cellular networks and large-scale wireless sensor networks. In this paper, an Optimal Backoff Time Interference Mitigation Algorithm (OBTIM) is proposed. This method performs rescheduling or channel switching when the performance of the WBANs falls below tolerance, utilizing the cell neighbour list established by the beacon method. Simulation results show that the proposed method improves the channel utilization and the network throughput, and in the meantime, reduces the collision probability and energy consumption, when compared with the contention-based beacon schedule scheme.

Wireless Body Area Network (WBAN) is characterized by intensive and highly mobile deployments, especially in the warding areas or public places where the network density can become very high [

Recent years have seen many researchers working on network interference between the cellular network and the wireless sensor networks. For example, in the case of a cellular network, the interference cancellation technique of WLANs based on the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) interference compensation mechanism is proposed and studied [

In this work, we design an Optimal Backoff Time Interference Mitigation Algorithm (OBTIM) for body area networks to address the aforementioned challenges. The method includes mechanisms of network interference detection, the asynchronous neighbour discovery method, and transmission rescheduling. The novelty of this method is that a method of backoff time optimization based on linear programming is proposed to increase the throughput and the asynchronous neighbour discovery method is proposed to establish a neighbour information table to help in the arrangement of dynamic retransmission and switching of channels according to the channel states. These actions will execute only if excessive interference is detected and will stop to continue regular data transmission after interference mitigation. By doing so, we minimize the time delay and energy consumption. The simulation results show that the OBTIM proposed in this paper outperforms the scheme based on beacon scheduling [

The OBTIM has less time delay and collisions. The time delay will increase significantly in the competition-based beacon scheme [

Compared with those algorithms without optimization (the competition-based beacon scheme and the scheme based on 802.15.4), the OBTIM has less throughput and average energy consumption since the backoff time optimization method based on linear programming is used to find the backoff time to minimize the system throughput. We know that the scheduling operation includes a data transmission delay _{,} and

The advantages of the OBTIM are as follows: (1) short backoff time and low time delay; (2) the lowest probability of beacon conflict; (3) under different scenarios of WBAN number and channel number, the method in this paper has a better throughput; and (4) the average energy consumption of a successful transmission of a packet is significantly lower than the other two schemes.

The rest of this paper is organized as follows. Section

The existing interference mitigation strategies mainly include techniques and algorithms in a frequency domain, power control, and cooperative communication.

In the frequency domain, technologies such as frequency band allocation, frequency domain analysis, and modulation are used to realize interference mitigation. González-Valenzuela et al. [

Power control is a very important technology in multiple access wireless networks for interference suppression. However, the centralized power control scheme often used in mobile cellular networks is not suitable for the distributed and independent WBANs. Wu et al. [

Cooperative communication is another technology that can effectively mitigate interference in dense WBAN deployment. The advantage of cooperative communication lies in spatial diversity. When the transmission distance between the source and the host nodes is large, or the radio condition becomes severe, the transmission reliability and energy efficiency can be improved significantly through cooperative communication [

Kim et al. [

Considering the radio channel characteristics of body area networks, we adopt an optimal backoff time-based internetwork interference mitigation method. We take into consideration the periodicity of application data transmission in combined body area networks to reschedule or switch the channel in case of internetwork interference, hence improving the transmission reliability with great effect.

Figure

Health service system based on WBAN.

Figure

Superframe model with the beacon.

We consider a typical wireless body area network (e.g., the one shown in Figure

Figure

The transmission status table establishing procedure.

When

We aim to find the corresponding empty time duration (Collision-Free Duration (CFD)) on the appropriate channel

The interference mitigation algorithm based on optimal backoff time is shown in Figure

Flow chart of the internetwork interference mitigation method.

As shown in Figure

The implementation process of the internetwork interference mitigation method.

We make the following assumptions:

Nodes cannot send or receive information simultaneously, but at any given time, one node performs either a sending or receiving function. To a node, the broadcasts transmitted from its neighbours are received error-free

Each node is allocated a unique identifier, and it is aware of it

We assume there are

Node

Node

Let us suppose there are

Determine the slot length.

Let

Find the neighbours.

During the receiving state, the node turns on its receiver and decodes its input. This input is processed by assuming that the message is received error-free. After the transmitter identity in the message is known and found not within the node’s neighbour list, it will be added, and if there is any new information, it will be updated at the receiver.

Let us analyse the Asynchronous Neighbour Discovery Method (ANDM) so as to facilitate further derivations.

Since there are a finite set of nodes and their neighbours are also finite, so there will be a finite set of relations. If nodes

Let

As we have already assumed synchronization, so it is sufficient not to consider message repetition, so let

Let us also assume that

It is assumed that node

In Table

The timeslot and state of node

Timeslot | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | ⋯ | |
---|---|---|---|---|---|---|---|---|---|---|

Node |
⋯ | |||||||||

Neighbour 1 | ⋯ | |||||||||

Neighbour 2 | ⋯ | |||||||||

Neighbour 3 | ⋯ | |||||||||

⋮ | ⋮ | |||||||||

Neighbour |
⋯ |

Let

As all the nodes are transmitting independently, the times that a neighbour is heard is uniformly distributed between 0 and

Each timeslot is a trial in which neighbours might be heard when

For an arbitrary

Set

As mentioned in Section

We make an assumption that all the WBANs in the system have the same transmission time

With regards to the transmission delay

Each WBAN has three states, namely, the interference transmission state, the execution state, and the normal transmission state. WBAN is converted in these three states accordingly. When interference occurs, WBAN transmission could be affected severely, which will start the rescheduling algorithm to find a suitable channel; after interference reduces, the system is back to normal operations until the next interference comes.

Assuming the system has already run the

The throughput

To avoid a conflict, each scheduling operation includes a data transfer delay

Substituting formulas (

It can be seen from formula (

The Lagrangian of this question is as follows:

In this situation, the optimal solution

Given that

Apparently

Assume

In the rescheduling phase, if the current channel is fully occupied, the rescheduling algorithm cannot obtain the rescheduling data transfer time of the current channel. It will first find a channel that has timeslots.

We assume that each WBAN contains a coordinator and a sensor node. The physical layer parameters were set according to the standard of IEEE802.15.4. The interbody path loss model is considered, and the path loss exponent is 2.4 with a shadowing standard deviation of 6 dB. We choose superframe length

The simulation parameter settings.

Parameter name | Transmission power (dBm) | Mobile speed interval (m/s) | Motion interval (s) | Pause interval (s) | Direction interval (degree) | Simulation duration (s) | Superframe duration (SD) (s) | Maximum tolerable delay(s) | Content window (CW) |
---|---|---|---|---|---|---|---|---|---|

Value | -10 | (0.2, 2.2) | (2, 6) | (0, 6) | (-180, 180) | 1000 | 0.1 | 0.15 | (1, 8) |

We assume that each WBAN user occupies an area of 5~10 square meters, with 5 randomly moving users in the

We can find that with the increase in the number of neighbours and the traffic load of WBAN, the interference will increase. This will lead to more beacon loss. It can be seen from Figure

The ratio of undiscovered WBANs to neighbouring WBANs.

Figure

Rescheduling delay for three different scenarios.

Figure

The ratio of average delay to the beacon interval.

The beacon collision probability in three schemes is compared in Figure

Collision probability of beacon comparison.

Figure

Throughput versus traffic load for three scenarios.

5 WBANs in a single channel

10 WBANs in a single channel

20 WBANs in double channels

As shown in Figure

Comparison of per-packet energy consumption (10 WBANs per single channel).

In this paper, a distributed internetwork interference mitigation scheme is proposed for body area sensor networks. The scheme takes into account entirely the low utilization rate of the network channel and adopts the scheduling strategy based on the optimal backoff time, so that the transmission time and channel can be selected reasonably when the network is disturbed: (1) when the channel utilization is low, the body area network is rescheduled by the coordinator on a free timeslot, and (2) when the current channel is fully occupied, the coordinator switches the channel in time. Simulation results show that the proposed approach of OBTIM outperforms the 802.15.4 base scheme and the competition-based signal scheme in producing fewer collisions, higher throughput, and lower energy consumption. Furthermore, when the density of the WBANs increases, the proposed method enables the channel switch to make reasonable adjustments to the transmission condition, to ensure the reliability of data transmission.

The data used to support the findings of this study are available from the corresponding author upon request.

The authors declare that there is no conflict of interest regarding the publication of this paper.

This work was supported by the National Natural Science Foundation of China (No. 61971248), the International Science and Technology Cooperation Programme (No. 2016D10008), the Ningbo Key Science and Technology Plan (2025) Project (2018B10075, 2019B10125, and 2019B10028), and the Key Science and Technology Projects of Zhejiang Province (2020C03064).