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AIR INTERFACE FOR FIXED BROADBAND WIRELESS ACCESS SYSTEMS

IEEE Std 802.16-2001

n = (Symbol Rate x Frame Duration)/4

 

Downlink Subframe

Uplink Subframe

 

PS 0

Adaptive

PS n-1

...

Frame j-2

Frame j-1

Frame j

Frame j+1

Frame j+2

...

Figure 38—TDD frame structure

6.2.7.4 Downlink map

The Downlink Map (DL-MAP) message defines the usage of the downlink intervals for a burst mode physical layer.

6.2.7.5 Uplink map

The uplink map (UL-MAP) message defines the usage for the uplink minislots using a series of IEs, which define the usage of each uplink interval. The UL-MAP defines the uplink usage in terms of the offset from the previous IE start (the length) in numbers of minislots.

6.2.7.5.1 Uplink timing

The uplink timing is based on the Uplink Time Stamp reference, which is a counter that increments at a rate that is 16 times the PS rate. It therefore has a resolution that equals 1/16 of the PS duration. This allows the SS to track the BS clock with a small time offset.

6.2.7.5.1.1 Uplink timing with unframed PHY

In the case of an unframed PHY, the downlink map (DL-MAP) message broadcasts the Uplink Time Stamp value to all SSs. The Uplink Time Stamp from the BS is then used to adjust the SS’s internal Time Stamp so that it tracks the BS timing. The SS Time Stamp is offset from the BS Time Stamp by the Timing Adjustment sent to each SS in the RNG-RSP message. The offset causes the uplink bursts to arrive at the BS at the proper time. After either the BS Time Stamp or SS Time Stamp reaches the maximum value of 229 – 1, the Time Stamp rolls over to zero and continues to count.

6.2.7.5.1.2 Uplink timing with framed PHY

In a framed PHY, there is no need for an Uplink Time Stamp counter as the uplink timing is referenced from the beginning of the downlink subframe. The Allocation Start Time in the UL-MAP is referenced from the start of the downlink subframe and may be such that the UL-MAP references some point in the current or

Copyright © 2002 IEEE. All rights reserved.

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