Essay About Scheduling Mechanism And Update Interval U

Techniques to Improve Blueooth Performance in Interference Environments
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Techniques to Improve Blueooth Performance in
Interference Environments
Nada Golmie and Nicolas Chevrollier
National Institute of Standards and Technology
Gaithersburg, Maryland 20899
Email: [email protected]
Abstract–Bluetooth is a radio technology for Wireless Personal Area Networks
operating in the 2.4 GHz ISM band. Since both Bluetooth and IEEE
802.11 devices use the same frequency band and may likely come together in
a laptop or may be close together at a desktop, interference may lead to significant
performance degradation. The main goal of this paper is to propose
solutions to the interference problem consisting of power control adjustments
and scheduling policies to be implemented by the Bluetooth device. Simulation
results are given for selected scenarios and configurations of interest.
Keywords–Bluetooth, Interference, Power Control, MAC scheduling
I. INTRODUCTION
The Bluetooth [1] technology is an emerging short range cable
replacement protocol operating in the 2.4 GHz ISM band.
Since both the Bluetooth and the IEEE 802.11 [2] protocols
operate in the 2.4 GHz, it is anticipated that interference may
severely degrade the performance of both systems.
Our goal is to propose solutions to the interference problem
pertaining to the Bluetooth radio operating in proximity to an
IEEE 802.11 network. We assume that the source of interference
to the Bluetooth system is an IEEE 802.11 system operating
in a direct sequence spread spectrum (DSSS) mode. In the
rest of this sequel, the terms IEEE 802.11 DSSS and WLAN
will be used interchangeably.
We investigate two techniques aimed at alleviating the interference
problem for Bluetooth. One technique is based on controlling
the transmitted power and keeping it proportional to the
signal-to-interference ratio (SIR) measured at the receiver. The
other technique takes advantage of the frequency hopping sequence
of Bluetooth and uses scheduling with the aim of avoiding
interference. Simulation results for scenarios of interest are
discussed. Performance is measured in terms of the mean access
delay, the probability of packet loss, and the transmitted
power.
This paper is organized as follows. In sections II and III,
we describe the distributed power control algorithm and the
scheduling mechanism respectively and give numerical results.
Concluding remarks are offered in section IV.
II. POWER CONTROL
Given that some devices provide the ability to dynamically
modify their transmission power, we would like to investigate
the dynamics of a power control (PC) strategy as a means of
alleviating the impact of interference.
We use a distributed algorithm to implement a PC procedure.
The basic idea is to adjust the interference level in the system to
no more than what is needed. We assume that the receiver does
not have any knowledge of other systems except for the system
it is communicating with. Interference from other systems is
measured in terms of the SIR level at the receiver. Note that SIR
is a wide-spread link quality measure and has been used in many
previous studies for power control and dynamic channel allocation
for interference limited systems [3] [4] [5]. The power
update algorithm works as follows. Initially, P0 = Pmax, then
every update interval U, the power at the transmitter, P(t + 1)
is updated as follows:
P(t + 1) = min(Pmax; max(Pmin;
SIR(t)
P(t)) (1)
where (t) is the target SIR and SIR(t) is based on an average
value over many measurements. The power update rule
takes into consideration the SIR(t) statistic measured at the receiver
side. The receiver can then relay this information to the
transmitter every update interval U.
Implementation Considerations Although the exact details
of a power control algorithm have been left undefined for the
most part, the Bluetooth specifications have included the necessary
hooks in the protocol in order to implement a power control
algorithm. Furthermore, the Bluetooth specifications classifies
devices into three power classes as summarized in Table I
TABLE I
BLUETOOTH DEVICE POWER CLASSES
Power Class Maximum Output Power Minimum Output Power