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参数资料
| 型号： | HFA3860BIV |
| 厂商： | HARRIS SEMICONDUCTOR |
| 元件分类： | 无绳电话/电话 |
| 英文描述： | 3.3V 288-mc CPLD |
| 中文描述： | TELECOM, CELLULAR, BASEBAND CIRCUIT, PQFP48 |
| 文件页数： | 17/40页 |
| 文件大小： | 272K |
| 代理商： | HFA3860BIV |
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4-17
Clear Channel Assessment (CCA) and
Energy Detect (ED) Description
The clear channel assessment (CCA) circuit implements the
carrier sense portion of a carrier sense multiple access
(CSMA) networking scheme. The Clear Channel
Assessment (CCA) monitors the environment to determine
when it is feasible to transmit. The result of the CCA
algorithm is available 16
μ
s after RX_PE goes high through
output pin 32 of the device. The CCA circuit in the
HFA3860B can be programmed to be a function of RSSI
(energy detected on the channel), carrier detection, or both.
The CCA output can be ignored, allowing transmissions
independent of any channel conditions. The CCA in
combination with the visibility of the various internal
parameters (i.e., Energy Detection measurement results),
can assist an external processor in executing algorithms that
can adapt to the environment. These algorithms can
increase network throughput by minimizing collisions and
reducing transmissions liable to errors.
There are two measures that are used in the CCA
assessment. The receive signal strength (RSSI) which
measures the energy at the antenna and carrier sense early
(CSE). Both indicators are normally used since interference
can trigger the signal strength indication, but it might not
trigger the carrier sense. The carrier sense, however,
becomes active only when a spread signal with the proper PN
code has been detected, so it may not be adequate in itself.
The CCA compares these measures to thresholds at the end
of the first antenna dwell following RX_PE going active. The
state of CCA is not guaranteed from the time RX_PE goes
high until the CCA assessment is made. At the end of a
packet, after RXPE has been deasserted, the state of CCA is
also not guaranteed. CCA should be sampled 16
μ
s after
raising RX_PE.
The receive signal strength indication (RSSI) measurement
is an analog input to the HFA3860B from the successive IF
stage of the radio. The RSSI A/D converts it within the
baseband processor and it compares it to a programmable
threshold. This threshold is normally set to between -70
and -80dBm. A MAC controlled calibration procedure can
be used to optimize this threshold.
The CSE (Carrier Sense Early) is a signal that goes active
when SQ1 (after an antenna dwell) has been satisfied. It is
called early, since it is indicated before the carrier sense used
for acquisition. It is calculated on the basis of the integrated
energy in the correlator output over a block of 15 symbols.
Thus, the CCA is valid after 16
μ
s has transpired from the time
RX_PE was raised.
The Configuration registers effecting the CCA algorithm
operation are summarized below (more programming details
on these registers can be found under the Control Registers
section of this document).
The CCA output from pin 32 of the device can be defined as
active high or active low through CR 1 (bit 5). The RSSI
thresholdissetthroughCR14.Ifthe actualRSSIvaluefrom the
A/D exceeds this threshold then ED becomes active.
The instantaneous RSSI value can be monitored by the
external network processor by reading the test bus in mode 3. It
measures the signal 16
μ
s after the start of each antenna or
data dwell. RSSI value is invalid after MD_RDY goes active if
CR31 bit 1 is set to a “1”. Value is valid until MD_RDY drops if
bit is set to a “0”. The programmable threshold on the CSE
measurement is set through CR12 and CR13. More details on
SQ1 are included in the receiver section of this document.
In a typical single antenna system CCA will be monitored to
determine when the channel is clear. Once the channel is
detected busy, CCA should be checked periodically to
determine if the channel becomes clear. CCA is stable to
allow asynchronous sampling or even falling edge detection of
CCA. Once MD_RDY goes active, CCA is then ignored for the
remainder of the message. Failure to monitor CCA until
MD_RDY goes active (or use of a time-out circuit) could result
in a stalled system as it is possible for the channel to be busy
and then become clear without an MD_RDY occurring.
A Dual antenna system has the added complexity that CCA
will potentially toggle between active and inactive as each
antenna is checked. The user must avoid mistaking the
inactive CCA signal as an indication the channel is clear. A
time-out circuit that begins with the first busy channel
indication could be used. Alternatively CCA could be
monitored, a clear channel indication for 2 successive
antenna dwells would show the channel clear on both
antennas. Time alignment of CCA monitoring with the
receivers 16
μ
s antenna dwells would be required. Once the
receiver has acquired, CCA should be monitored for loss of
signal until MD_RDY goes active.
An optional CCA mode is set by CR31 bit 0. When set to a
zero, the HFA3860B will perform the CCA monitoring for
successive antenna dwells when dual antenna mode is
selected. The external CCA signal will go active when a busy
channel is detected, CCA will stay active until the channel
shows clear for two successive antenna dwells. This allows
the same simple algorithm to be used in both signal and dual
antenna, namely, continuous monitoring of CCA for a clear
channel until MD_RDY goes active.
CR5 selects the starting antenna used when RXPE is
brought active.
CSE is updated at the end of each antenna dwell. After
acquisition, CSE is updated every 64 symbols. In the event
of signal loss after acquisition, CSE may go inactive. But
because the accumulation is over 63 symbols instead of 15,
it is more likely the SQ1 value will exceed the CSE threshold
and CSE will remain active.
HFA3860B
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PDF描述 |
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| HFA3860BIV96 | nullDirect Sequence Spread Spectrum Baseband Processor |
| HFA3861BIN | Direct Sequence Spread Spectrum Baseband Processor |
| HFA3861BIN96 | Direct Sequence Spread Spectrum Baseband Processor |
| HFA3925IA | null2.4GHz - 2.5GHz 250mW Power Amplifier |
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相关代理商/技术参数 |
参数描述 |
|---|---|
| HFA3860BIV WAF | 制造商:Harris Corporation 功能描述: |
| HFA3860BIV96 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| HFA3860IV | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Harris Corporation 功能描述: |
| HFA3860IV WAF | 制造商:Harris Corporation 功能描述: |
| HFA3860IV96 | 制造商:INTERSIL 制造商全称:Intersil Corporation 功能描述:11 Mbps Direct Sequence Spread Spectrum Baseband Processor |
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