User Guide

AB-Access Config & User Guide 5.5 Axxcelera Broadband Wireless
July 27, 2004 Company Confidential Page 24 of 129
5.4 Wireless MAC
When data is sent over the wireless link it must first be put into a structure that each end unit
will understand. The hardware that does this is called the MAC (Medium Access Controller).
RGFDHDR DACK DCELLATT STT RR UACK
UCELL/
UCELLR
5.4.1 Downstream burst
5.4.1.1 Access Point Turnaround Time (ATT)
AB-Access system is TDD (Time Division Duplexing), meaning that the AP and SUs
transmit and receive on the same frequency. It is therefore necessary to have a small delay between
the transmit and receive processes, because it is using the same hardware to perform both functions.
5.4.1.2 Frame Descriptor Header (FDHDR)
Downstream bursts begin with a Frame Descriptor Header (FDHDR) this portion of the
MAC frame is seen by all SUs in that sector. The FDHDR contains a map of all traffic upstream and
downstream, to occur within the MAC frame. This is why you assign a unit a MID, when an SU sees
an FDHDR it looks for its MID in the FDHDR to see if it is going to receive any cells. If it does not
see its MID it will ignore the rest of the frame.
5.4.1.3 Reservation Grant (RG)
The next field in the downstream burst is the Reservation Grant Response (RGR). An RGR is
a response to a Reservation Grant Request (Upstream Burst). The RGR acknowledges a request and
tells the SU that it can transmit on the upstream burst.
A
SU
SU
SU
AC
F R AC
Cell
Cell
down-stream up-stream
R-
-
-
Cell Cell
-
idlidl
Variable length MAC