參數(shù)資料
型號(hào)： MQ80C52CXXX-20/883R
廠商： ATMEL CORP
元件分類(lèi)： 微控制器/微處理器
英文描述： 8-BIT, MROM, 20 MHz, MICROCONTROLLER, CQFP44
封裝： CERAMIC, QFP-44
文件頁(yè)數(shù)： 67/101頁(yè)
文件大小： 3398K
代理商： MQ80C52CXXX-20/883R
91
8168C-MCU Wireless-02/10
AT86RF212
6.8 Link Quality Indication (LQI)
6.8.1 Requirements
The IEEE 802.15.4 standard defines the LQI as a characterization of the strength
and/or quality of a received frame. The use of the LQI result by the network or
application layer is not specified in this standard. The LQI value shall be an integer
ranging from 0 to 255, with at least 8 unique values. The minimum and maximum LQI
values (0 and 255) should be associated with the lowest and highest quality compliant
signals, respectively, and LQI values in between should be uniformly distributed
between these two limits.
6.8.2 Implementation
During symbol detection within frame reception, the AT86RF212 uses correlation
results of multiple symbols in order to compute an estimate of the LQI value. This is
motivated by the fact that the mean value of the correlation result is inversely related to
the probability of a detection error.
LQI computation is automatically performed for each received frame, once the SHR has
been detected. LQI values are integers ranging from 0 to 255 as required by the IEEE
802.15.4 standard.
6.8.3 Obtaining the LQI Value
The LQI value is available, once the corresponding frame has been completely
received. This is indicated by the interrupt IRQ_3 (TRX_END). The value can be
obtained by means of a frame buffer read access, see section 4.3.2.
6.8.4 Remarks
The reason for a low LQI value can be twofold: a low signal strength and/or high signal
distortions, e.g. by interference and/or multipath propagation. High LQI values,
however, indicate a sufficient signal strength and low signal distortions.
Note that the LQI value is almost always 255 for scenarios with very low signal
distortions and a signal strength much greater than the sensitivity level. In this case, the
packet error rate tends towards zero and increase of the signal strength, i.e. by
increasing the transmission power, cannot decrease the error rate any further.
Received signal strength indication (RSSI) or energy detection (ED) can be used to
evaluate the signal strength and the link margin.
ZigBee networks often require identification of the “best” routing between two nodes.
LQI and RSSI/ED can be applied, depending on the optimization criteria. If a low frame
error rate (corresponding to a high throughput) is the optimization criteria, then the LQI
value should be taken into consideration. If, however, the target is a low transmission
power, then the RSSI/ED value is also helpful.
Various combinations of LQI and RSSI/ED are possible for routing decisions. As a rule
of thumb, information on RSSI/ED is useful in order to differentiate between links with
high LQI values. However, transmission links with low LQI values should be discarded
for routing decisions, even if the RSSI/ED values are high, since it is merely an
information about the received signal strength, whereas the source can be an interferer.
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