User's Manual

12 MDS Mercury 16E Technical Manual MDS 05-6302A01, Rev. B
There are two operating modes that the Mercury supports. The first
mode is Matrix A in which the Mercury uses Space-Time Coding (STC)
on the transmitter to allow it to send the same data on each channel but
coded differently in order to get transmit diversity. On the receive side,
the Mercury transceiver uses Maximum Ratio Combining (MRC) to
more accurately reconstruct the received signal by using both receive
channels.
The second mode is Matrix B in which the Mercury uses Spatial
Multiplexing (SM) to send different data flows on each channel
allowing it to effectively double the amount of data transmitted. The
Mercury offers a Matrix A/B setting in which the transceivers determine
in real time which mode, Matrix A or Matrix B, to use according to the
channel conditions. This determination is made based on the SNR and
Packet Error Rate (PER).
GE MDS sells antennas that are dual-polarized for MIMO applications.
This includes sector antennas for Base Stations and panel antennas for
Subscribers. Each antenna has two feed lines, one for the vertically
polarized element, and one for the horizontally polarized element.
3.3 ARQ and Hybrid ARQ
Automatic Retransmission Request (ARQ) enables retransmission of
erroneous or lost data packets. Hybrid ARQ (HARQ) combines forward
error correction with ARQ retransmissions to improve performance at
lower RF signal levels.
With ARQ, the receiver discards erroneous packets and requests
retransmission. With HARQ, erroneous packets are saved by the
receiver and combined with the retransmitted data. Generally, HARQ
provides better throughput than ARQ. While ARQ and HARQ can be
enabled at the same time, it is not recommended to do so because
throughput will be less than if either ARQ or HARQ was enabled on its
own.
ARQ and HARQ can be enabled or disabled in the ARQ/HARQ Settings
table of the
Configuration-Radio page on the Base Station.
ARQ Setup
ARQ utilizes a sliding window approach where a “window” of blocks
can be transmitted without receiving acknowledgement from the
receiver. ARQ blocks that are unacknowledged will be resent. You can
specify the block and window size at the Base Station, as well as Block
Lifetime, Transmitter Delay, and Receiver Delay.
• ARQ Block Size - The size, in bytes, of the block of data to be
considered for retransmission.