Rainbow Electronics ATmega128RFA1 - Manual (Page 88)

88
8266A-MCU Wireless-12/09
ATmega128RFA1
9.8.2.5 High Data Rate Mode Options
Receiver Sensitivity Control
The different data rates between PPDU header (SHR and PHR) and PHY payload
(PSDU) cause a different sensitivity between header and payload. This can be adjusted
by defining sensitivity threshold levels of the receiver. The receiver does not receive
frames with an RSSI level below the defined sensitivity threshold level (register bits
RX_PDT_LEVEL > 0). Under these operating conditions the receiver current
consumption is reduced by 500 µA (refer to chapter
"Current Consumption
Specifications" on page 509 ).
A description of the settings to control the sensitivity threshold with register RX_SYN
can be found in section
"RX_SYN – Transceiver Receiver Sensitivity Control Register"
on page 118 .
Reduced Acknowledgment Timing
On higher data rates the IEEE 802.15.4 compliant acknowledgment frame response
time of 192 µs significantly reduces the effective data rate of the network. To minimize
this influence in Extended Operating Mode RX_AACK (see section
"RX_AACK_ON –
Receive with Automatic ACK" on page 46 ), the acknowledgment frame response time
can be reduced to 32 µs. Figure 9-32 below illustrates an example for a reception and
acknowledgement of a frame with a data rate of 2000 kb/s and a PSDU length of 80
symbols. The PSDU length of the acknowledgment frame is 5 octets according to
IEEE 802.15.4.
Figure 9-32. High Data Rate AACK Timing
0 time [µs] 192 512
AACK_ACK_TIME = 0 PSDU: 80 octets
S
F
D
P
H
R
S
F
D
P
H
R
704 916
32 µs
PSDU: 80 octets
S
F
D
P
H
R
S
F
D
P
H
R
192 µs
544
AACK_ACK_TIME = 1
ACK
ACK
The acknowledgment time is reduced from 192 µs to 32 µs if bit AACK_ACK_TIME of
register XAH_CTRL_1 is set.
9.8.3 Antenna Diversity
The main features of the Antenna Diversity implementation are:
• Improves signal path robustness between nodes;
• Self-contained antenna diversity algorithm of the radio transceiver;
• Direct register based antenna selection;
9.8.3.1 Overview
The receive signal strength may vary and affect the link quality even for small changes
of the antenna location due to multipath propagation effects between network nodes.
These fading effects can result in an increased error floor or loss of the connection
between devices.
Antenna Diversity can be applied to reduce the effects of multipath propagation and
fading hence improving the reliability of a RF connection between network nodes.