Elsevier

Computer Networks

Volume 51, Issue 12, 22 August 2007, Pages 3338-3353
Computer Networks

Mutual interference analysis of IEEE 802.15.4 and IEEE 802.11b

https://doi.org/10.1016/j.comnet.2007.01.034Get rights and content

Abstract

IEEE 802.15.4 and IEEE 802.11b, operating in the 2.4 GHz unlicensed industrial scientific medical (ISM) frequency band, may lead to signal interference and result in significant performance degradation when devices are collocated in the same environment. The main goal of this paper is to evaluate the effect of mutual interference on the performance of IEEE 802.15.4 and IEEE 802.11b systems. An analytic model for interference between IEEE 802.15.4 and IEEE 802.11b is suggested. The packet error rate (PER), transmission delay, and throughput are evaluated for IEEE 802.15.4 and IEEE 802.11b. The power spectral density of the IEEE 802.11b is considered in order to determine in-band interference power of the IEEE 802.11b to the IEEE 802.15.4. The simulation results by OPNET are shown to validate the numerical analysis.

Introduction

Recently, a low rate wireless personal area network (LR-WPANs), IEEE 802.15.4, has been standardized [1], [2]. The goal of the IEEE 802.15.4 is to provide a standard, which has the characteristics of ultra-low complexity, low-cost and extremely low-power for wireless connectivity among inexpensive, fixed, and portable devices such as sensor networks and home networks. To provide the global availability, the IEEE 802.15.4 devices use the 2.4 GHz industrial scientific and medical (ISM) unlicensed band. The proliferation of mobile computing devices including laptops, personal digital assistants (PDAs), and wearable computers has created a demand for wireless personal area networks (WPANs).

Today, most radio technologies considered by the WPANs including Bluetooth [3] and IEEE 802.15.4 employ the 2.4 GHz ISM frequency band, which is also used by Local Area Network (WLAN) devices implementing the IEEE 802.11b standard specifications [4]. It is anticipated that some interference will result from all these technologies operating in the same environment. The IEEE 802.11b WLAN devices operating in proximity to the IEEE 802.15.4 devices may significantly impact the performance of the IEEE 802.15.4 WPAN and vice versa.

For example, the IEEE 802.15.4 is used for a sensor and control network and the IEEE 802.11b is used for a audio/video (A/V) network within a home. When a notebook is capable of supporting these two standards, the coexistence distance may be smaller than 1 m. Therefore, the performances of the IEEE 802.15.4 and IEEE 802.11b needs to be evaluated when they operate in proximity to each other.

Some related researches study the coexistence problem between the IEEE 802.15.4 and the 802.11b [5], [6], [7], [9]. In [5], the packet error rate (PER) of the IEEE 802.15.4 under the IEEE 802.11b and the IEEE 802.15.1 (Bluetooth [10]) is obtained by experiments only. In [6], more accurate measurements such as receiver signal strength indicator, PER, throughput of the IEEE 802.15.4 are performed. The impact of an IEEE 802.15.4 network on the IEEE 802.11b devices is analyzed in [7] based on [8]. Here, the PER is assumed to be identical to the collision probability, which is a probability that an IEEE 802.11b packet is collided by one or multiple IEEE 802.15.4. However, the collision between the IEEE 802.11b packet and the IEEE 802.15.4 packet does not always cause packet loss. Moreover, the PER of the IEEE 802.15.4 packets by the interference of IEEE 802.11b is not considered. In [9], the PER of IEEE 802.15.4 under the interference of IEEE 802.11b is evaluated using simulation. However, the interference of IEEE 802.15.4 to IEEE 802.11b is not considered. To the best knowledge of the authors, the interference analysis between the IEEE 802.15.4 and the IEEE 802.11b has not been reported yet in the literature.

In this paper, the performances of the IEEE 802.15.4 and the IEEE 802.11b under the mutual interference are analyzed. The PER, average transmission delay, and throughput are used as performance measures. The PER is obtained from the bit error rate (BER) and the collision time. The BER is obtained from signal to interference and noise ratio (SINR). The collision time is defined as the time that a desired packet experiences the interference by interfering packet(s). For accurate analysis, in-band interference power ratio of the IEEE 802.11b is obtained from the power spectral density of the IEEE 802.11b and the frequency offset. The frequency offset is defined as the difference between the center frequencies of the IEEE 802.15.4 and the IEEE 802.11b. An average transmission delay is defined as the total time from a channel access moment by a source station to the time to receive an ACK packet transmitted by a destination station. The throughput is the amount of data transferred from one station to another station during a specified amount of time. The throughput is calculated from the PER and the average transmission delay. The analytic results are compared with the simulation results.

This paper is organized as follows. Section 2 briefly overviews the IEEE 802.15.4 and IEEE 802.11b. In Section 3, the BER of the IEEE 802.15.4 and the IEEE 802.11b using SINR is evaluated. Section 4 describes the interference model of the IEEE 802.15.4 and the IEEE 802.11b. The performances are analyzed in Section 4. In Section 5, comparisons between analytic and simulation results are shown. Finally, this paper concludes in Section 6.

Section snippets

IEEE 802.15.4 overview

A new IEEE standard, 802.15.4, defines both the physical layer (PHY) and medium access control (MAC) sublayer specifications for low-rate wireless personal area networks (LR-WPANs), which support simple devices that consume minimal power and typically operate in the personal operating space (POS) of 10 m or less [1]. Two types of topologies are supported in the IEEE 802.15.4: a one-hop star or a multi-hop peer-to-peer topology. The network and upper layers are defined by the ZigBee Alliance [12].

Bit error rate evaluation of IEEE 802.15.4 and WLAN

The PHY of the IEEE 802.15.4 at 2.4 GHz uses offset quadrature phase shift keying (OQPSK) modulation with half-sine pulse shaping, which is equivalent to MSK [13]. Denote the Eb/No be the ratio of the average energy per information bit to the noise power spectral density at the receiver input, assuming an additive white Gaussian noise (AWGN) channel. Then the bit error rate (BER) of OQPSK, bOQPSK, can be expressed asbOQPSK=Q2γEbNo,Q(x)=12πxexp-u22du,where γ  0.85 [13].

The PHY of the WLAN uses

Performance analysis of IEEE 802.15.4 and IEEE 802.11b

Fig. 4 shows a model for coexistence, where WLAN and IEEE 802.15.4 can interfere with each other.

Each network consists of two nodes. WLAN_0 and WLAN_1 form the WLAN network. The distance between WLAN_0 and WLAN_1 is d(W_0, W_1). IEEE 802.15.4 network consists of one Coorinator and one End_device with d(Coor, End) apart.

Comparative evaluations

For simulation, the slotted CSMA/CA of the IEEE 802.15.4 model is developed using OPNET. The length of LOS, d0, is 8 m and the path loss exponent, n, is 3.3. The parameters for the simulation and the analysis are shown in Table 2.

Conclusion

In this paper, the performances of IEEE 802.15.4 and IEEE 802.11b operating in the 2.4 GHz ISM band are evaluated based on MAC and PHY layer models for both systems. The packet error rate (PER), transmission delay, and throughput are used as the performance metrics for both systems. The PER is obtained from the bit error rate (BER) and the collision time. The collision time is calculated under assumption that the packet transmissions of the IEEE 802.15.4 and the IEEE 802.11b are independent.

Soo Young Shin is a Student Member of IEEE since 2004 and was born in 1975. He received his B.S. and M.S. degrees in Electrical Engineering and Computer Science from Seoul National University, Korea in 1999, and 2001, respectively. Now he is a Ph.D. candidate. His current research interest is wireless packet networks such as WLAN, Bluetooth, ZigBee including performance and interference analysis of Bluetooth, ZigBee and WLAN.

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Soo Young Shin is a Student Member of IEEE since 2004 and was born in 1975. He received his B.S. and M.S. degrees in Electrical Engineering and Computer Science from Seoul National University, Korea in 1999, and 2001, respectively. Now he is a Ph.D. candidate. His current research interest is wireless packet networks such as WLAN, Bluetooth, ZigBee including performance and interference analysis of Bluetooth, ZigBee and WLAN.

Hong Seong Park was born in Korea in 1961. He received his B.S., M.S. and Ph.D. degrees from Seoul National University, Korea in 1983, 1986, and 1992, respectively. Since 1992, he has been professor in the Department of Electrical and Computer Engineering, Kangwon National University, Korea. His research interests include the design and analysis of communication networks and mobile/wireless communication, discrete event systems, and network-based control systems.

Wook Hyun Kwon was born in Korea on January 19, 1943. He received his B.S. and M.S. degrees in Electrical Engineering from Seoul National University, Seoul, Korea, in 1966 and 1972, respectively. He received his Ph.D. degree from Brown University, Providence, RI, in 1975. From 1976 to 1977, he was an adjunct Assistant Professor at the University of Iowa, Iowa City. Since 1977, he has been with the School of Electrical Engineering, Seoul National University. From 1981 to 1982, he was a Visiting Assistant Professor at Stanford University, Stanford, CA. Since 1991, he has held the position of Director of the Engineering Research Center for Advanced Control and Instrumentation. His main research interests currently include multivariable robust and predictive controls, statistical signal processing, discrete event systems, and industrial networks.

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