Figure 57 MAC Frame Structure for Sectored Antennas
|
BCH |
BCH |
BCH |
FCH |
FCH |
J FCH |
PCH |
DL DL |
|
1 |
2 |
N |
1 |
2 |
N |
1 |
1 2 |
|
ul |
la |
ul] |
rch |
rch |
rch |
|
1 |
2 |
u |
1 |
2 |
n |
|
MAC frame (hi) |
MAC frame (i) |
MAC frame (i+1 ) |
MAC frame{ยก1-1} |
The MAC frame consists of: Broadcast Channel (BCH) duration, Frame Control Channel (FCH) duration, Access Feedback Channel (ACH) duration and at least one Random Channel (RCH) duration. If there is transmission between the AP/CC and the MTs, the Downlink (DL) phase and/or Uplink (UL) phase are included in the MAC frame. If there is transmission among the MTs (direct mode), the Direct Link (DiL) phase is also included. The BCH duration is fixed. The duration of the FCH, DL, DiL, and UL phases and the number of RCHs are dynamically determined by the AP/CC.
The BCH, FCH, ACH, and RCH contain control messages, whereas the DL phase, DiL phase, and UL phase mostly contain user data and certain control messages. The standard defines the message format through the transport and logical channels. There are six transport channels (with three letter abbreviations):
1. Broadcast Channel (BCH)
2. Frame Channel (FCH)
3. Access Feedback Channel (ACH)
4. Long Transport Channel (LCH)
5. Short Transport Channel (SCH)
6. Random Access Channel (RCH)
There are ten logical channels (with four letter abbreviations):
1. Broadcast Control Channel (BCCH)
2. Frame Control Channel (FCCH)
3. Random Access Feedback Channel (RFCH)
4. User Data Channel (UDCH)
5. User Multicast Channel (UMCH)
6. User Broadcast Channel (UBCH)
7. RLC Broadcast Channel (RBCH)
8. Dedicated Control Channel (DCCH)
9. Link Control Channel (LCCH)
10. Association Control Channel (ASCH)
Figure 5.8 illustrates the MAC frame structure, the transport and logical channels and their relationships. All messages are mapped to specific logical channels based on their content and their functionality. The messages are constructed according to a format defined by the logical channel. Then the messages will pass to the transport channel to receive the appropriate transport services.
Figure 5.8. MAC Frame Structure, Transport Channel, and Logical
Channel
Figure 5.8. MAC Frame Structure, Transport Channel, and Logical
Channel
Each MT's MAC is uniquely identified by a MAC ID which was assigned by the AP's RLC during the association process. The HiperLAN/2 MAC is connection oriented. Before an application can transmit, it requires the MT to establish a connection with the AP's RLC. This RLC assigns to this connection a DLC Connection ID (DLCC ID). In the centralized mode (CM), the DLC User Connection ID (DUC ID), which is obtained as a combination between the MAC ID and the DLCC ID, uniquely identifies the connection in the cell. In distribution mode (DM), the definition of DUC ID is slightly different. DUC ID, which identifies the connection in DM mode, is the combination of source MAC ID, destination MAC ID, and DLCC ID. DUC ID is also used for identifying the control channels. DUC ID is essential for the AP to allocate bandwidth to a specific connection (both user data and control).
Post a comment