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WLAN Device with Variable Channel Clear Assessment Threshold

IP.com Disclosure Number: IPCOM000198272D
Original Publication Date: 2010-Aug-23
Included in the Prior Art Database: 2010-Aug-23
Document File: 3 page(s) / 286K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

WLAN (Wireless Local Area Network) systems based on the IEEE 802.11 standards (IEEE: Institute of Electrical and Electronic Engineers) employ a CSMA/CA (Channel Sense Multiple Access with Collision Avoidance) scheme for arranging access to the radio channel in a distributed way. As an important part of this scheme, each device wishing to access the channel will do a channel clear assessment (CCA) before transmitting. If the channel is found to be occupied the device will defer its transmission. The standard defines various modes for channel clear assessment, taking the detection of another WLAN signal, the RX (Receiver) power observed in the channel or a combination of both as criteria for declaring the channel busy. CCA is handled by the WLAN chipsets in hardware. In some practical scenarios with well-planned WLAN infrastructure and good coverage throughout the desired area, the high sensitivity of the CCA scheme as implemented in common chip sets can lead to undesirable effects. Interference from other systems may cause the WLAN devices to abstain from channel access even if the quality of the intended communication link is good enough to tolerate the interference level. Besides the non-deterministic impact on average channel access delay, which is of special concern for time-critical applications such as motion control, the sensitivity of the CCA mechanism also has strong impact on the system throughput in networks with multiple access points (APs) operating on the same channel.

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WLAN Device with Variable Channel Clear Assessment Threshold

Idea: Dr. Mattias Lampe, CN-Beijing; Jifeng Tian, PhD, CN-Beijing; Zhijun Li, CN-Beijing; Jörg

ards (IEEE: Institute of

      Access with
ted way. As an hannel clear
ied the device will defer its king the detection bination of both as ardware.

                                      age throughout the hip sets can lead to s to abstain from
h to tolerate the ich is of itivity of the CCA
rong impact on the system throughput in networks with multiple access points

red for declaring a dustrial

interface for

WLAN chip sets.

it is not possible to

tion of a WLAN signal,
Points reportedly

  many considerations, sible or unfeasible for a

llowing dynamic

                             (Data
.11. The solution introduces a digitally adjustable ceived signal strength

itecture for a WLAN chip set with separate RX and TX X switch, whereas Figure 2 shows a ort. Both cases

(Access Point)

rely on the CPU st computer

The scheme for choosing the best CCA threshold in a given scenario is outside the scope of this solution. In the following, it is assumed that the desired value for the CCA threshold has been determined by some entity and is known to the CPU.

The suggested CCA adjustment scheme can then be described as follows:

• The control logic shown in the figures is responsible for providing the control signals required for adjusting the digital attenuator. In the architecture according to Figure 2 (which is less preferable than the one in Figure 1) the control logic will autonomously (i.e. without CPU interaction) toggle the attenuation value between the lowest possible value (in TX mode) and the value corresponding to the desired CCA threshold (in RX mode). The control logic can distinguish

© SIEMENS AG 2010 file: 2010J11411.doc page: 1

Müller, DE-Karlsruhe

WLAN (Wireless Local Area Network) systems based on the IEEE 802.11 stand Electrical and Electronic Engineers) employ a CSMA/CA (Channel Sense Multiple Collision Avoidance) scheme for arranging access to the radio channel in a distribu important part of this scheme, each device wishing to access the channel will do a c assessment (CCA) before transmitting. If the channel is found to be occup transmission. The standard defines various modes for channel clear assessment, ta of another WLAN signal, the RX (Receiver) power observed in the channel or a com criteria for declaring the channel busy. CCA is handled by the WLAN chipsets in h

In some practical scenarios with well-planned WLAN infrastructure and good cover
desired area, the high sensitivity of the CCA scheme as implemented in common c undesirable effects. Interference from other systems may cause the WLAN device
channel access even if the quality of the intended communication link is good enoug interference level. Besides the non-deterministic impact on average channel access delay, wh special concern for time-critical applications such as motion control, the sens
mechanism also has st
(APs) operating on the same channel.

Reducing the sensitivity of the CCA th...