Wireless Future - Telenor

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Preamble BCH FCH ACHs
Preamble SCHs LCHs SCHs
Preamble LCHs SCHs LCHs
Preamble RCH
Figure 6 Structure of
the PDU trains
connection x connection y
3 Downlink PDU train;
4 Uplink PDU train with short preamble;
5 Uplink PDU train with long preamble;
6 Direct Link PDU train.
In this exercise non-sector antennas and centralised
mode are considered only (i.e. PDU train
2 and 6 are not considered). The structures of the
different PDU trains are shown in Figure 6.
4.1.1 Broadcast PDU Train
The preamble of the BCH is 4 OFDM symbols
(16 µs). P BCH = 4.
The BCH has a fixed length of 15 bytes, and
uses always PHY mode 1, i.e. 5 OFDM symbols:
LBCH = 15
3 =5
(3)
The FCH is built on fixed size IE (Information
Elements) blocks. The AP determines the number
of blocks. Each IE block contains three
information elements with a length of 8 octets
and a CRC of length 24 bits. The FCH length
equals:
�� �
�
2 · n · 8 216
LFCH =
·
(4)
24 NDBPS(FCH) where
LCHs
SCHs
Broadcast
• • • Downlink
• • • Uplink
Random
Access
N DBPS is data bits per OFDM symbol
n is the number of active connections (duplex).
The minimum length of the L FCH for non-sector
antennas is 9 OFDM symbols (36 µs). The ACH
has a fixed length of 9 bytes (uses always PHY
1 mode)
LACH = 9
3 =3
The overall size of the broadcast train is:
L BPT = P BCH + L BCH + L FCH + L ACH
(5)
(6)
4.1.2 Downlink PDU Train
The downlink and uplink PDU trains consist of
Short Channel (SCH) and Long Channel (LCH)
PDUs. The SCH PDU is 9 bytes long and carries
DLC control information such as ARQ acknowledgements
and resource request for next frame
(uplink only). The LCH PDU is 54 bytes long,
where 48 bytes are allocated to the payload and
the rest is used for DLC header.
The preamble of the Downlink PDU train is
2 OFDM symbols. MTs might have a number
of SCHs and LCHs per frame. The size of the
downlink PDU train excluding the LCH PDUs is
�
k�
�
�
jm · 72
LDPT = k · PDL +
(7)
NDBPS(SCH) �
where
k = number of active users
J m = number of SCH PDUs for user m.
In the simulations the SCH (i.e. ARQ protocols)
in the downlink is omitted. The size of the
downlink PDU train excluding the LCH PDUs
will then be:
L DPT = k ⋅ P DL
m=1
4.1.3 Uplink PDU Train
The preamble for an uplink PDU train is 3
(short) or 4 (long) OFDM symbols. Just as for
the downlink train MTs multiple of SCHs and
LCHs per frame. Notice that the order of the
LCH and SCH has been exchanged compared
to the downlink train.
(8)
The number of RCH slots r determines the RCH
size. Each slot has the length SCH (PHY 1) with
uplink preamble.
The size of uplink PDU train excluding LCH
PDUs is
�
k�
�
�
jm · 72
LUPT = k · PUL +
NDBPS(SCH) �
m=1
+ r . (3 + P UL ) (9)
In the simulations, one SCH is used per active
connections for resource request purposes. The
corresponding size of uplink PDU train excluding
LCH PDUs will be:
Telektronikk 1.2001