Image Processing Reference
In-Depth Information
25.6.2 Separation in the Time Domain
. IEEE .b carrier sensing algorithm could also consider Bluetooth and IEEE
../ZigBee signals
∗
as well as Bluetooth (and IEEE ../ZigBee) could be
extended with a carrier sensing algorithm [ZKJ]. he principle problem of carrier sens-
ing though is, that to be really effective, the transmitter has to sense the situation at the
receiver correctly, i.e., the correlation between transmitter and receiver situation has to
be high. In an uncoordinated WLAN-WPAN scenario, the hidden as well as the exposed
terminal problems are likely to countermeasure any advantage there might be.
. Joint scheduler can allot alternating transmit time shares to both systems in a (to be spec-
ified) fair way. his, of course, only works (and with AFH is necessary only) when both
systems are in one device, or even on one chip. Then again, such a measure might be a
necessity, when otherwise blocking would occur.
25.6.3 Separation in Space
. Should IEEE .b and Bluetooth or IEEE .. coexist in the same unit, an intel-
ligent antenna design and placement is necessary to optimize the isolation between the
antennas and to prevent blocking. This will not reduce collisions but minimizes their
impact by maximizing the CIRs for the two systems.
†
. Antenna diversity can help each of the technologies individually to improve its perfor-
mance.
25.7 Summary and Conclusions
When deciding on a wireless technology to use, first the characteristics of the foreseen applica-
tion have to be clarified: Are the units going to move with or within the network, is the mobility
range small or large, at what speed do the units move, is access needed to a large data base or just
locally,isbatterylifeacriticalissue,whatmaximumdistanceshouldthewirelesslinkcover,what
distance does it cover in average, etc.? As a next step, the existing technologies can be viewed for their
applicability.
Bluetooth is a comparably power efficient WPAN technology. Like all wireless systems it cannot
provide hard throughput guarantees. Bluetooth is nevertheless quite robust for best-effort traffic in
coexistence environments. One hundred Bluetooth piconets can transmit at an average data rate of
%
m
. Fifty fully loaded piconets can transmit at an average, uni-
directional transmission rate of kbps. Similar results are likely to be achieved on larger factory
floors (provided the piconet density is comparable), as the disadvantage of a larger number of units
can be outweighed by the more structured and predictable unit location. Bluetooth is the only of the
discussed technologies that supports voice well in addition to data transmission.
⋅
. kbps in an area of
×
∗
As has been mentioned before, the IEEE . specification already provides for the possibility that IEEE . senses
and not transmits if other systems than IEEE . systems are active [Insb, Section ...]. ...].This has been found to
give the best results in interfered environments [KAT]. Nevertheless, even this mechanism holds a principle problem:
IEEE . will refrain from transmission when it senses that another, near by system
transmits
.Toimprovecoexistence
though IEEE . should refrain from transmission when nearby units
receive
.
†
Helpful to minimize the interference power is of course also power control (when applied by the interfering unit). Never-
theless, even though it can be recommended to implement power control (let alone to save power [MZTM]), in real-life
situations it cannot be relied upon that the interfering unit can indeed live with less power.
