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AIR INTERFACE FOR FIXED BROADBAND WIRELESS ACCESS SYSTEMS

IEEE Std 802.16-2001

An SS receiving a Bandwidth Request Header on the downlink shall discard the PDU.

The fields of the Bandwidth Request Header are defined in Table 6. Every header is encoded, starting with the HT and EC fields. The coding of these fields is such that the first byte of a MAC header shall never have the value of 0xFX. This prevents false detection on the stuff byte used in the transmission CS.

 

 

Table 6—Bandwidth request header fields

 

 

 

Name

Length

Description

(bits)

 

 

 

 

 

 

 

Bandwidth Request

BR

16

The number of bytes of uplink bandwidth requested by the SS. The bandwidth request is for

 

 

the CID. The request shall not include any PHY overhead.

 

 

 

CID

16

Connection Identifier

 

 

 

EC

1

Always set to zero.

 

 

 

 

 

Header Check Sequence

HCS

8

An 8-bit field used to detect errors in the header. The generator polynomial is g(D)=D8 + D2

 

 

+ D + 1.

 

 

 

HT

1

Header Type = 1

 

 

 

Type

6

Indicates the type of bandwidth request header

 

 

 

6.2.2.2 MAC subheaders

Three types of MAC subheaders may be present. The per-PDU subheaders (the Fragmentation subheader and the Grant Management subheaders) may be inserted in MAC PDUs immediately following the Generic MAC Header if so indicated by the Type field. If both the Fragmentation and Grant Management subheaders are indicated, the Grant Management subheader shall come first.

The only per-SDU subheader is the Packing subheader. It may be inserted before each MAC SDU if so indicated by the Type field. The Packing and Fragmentation subheaders are mutually exclusive and shall not both be present within the same MAC PDU.

If present, all per-PDU subheaders shall always come before the first per-SDU subheader.

6.2.2.2.1 Fragmentation subheader

The Fragmentation subheader (FSH) is shown in Table 7.

Table 7—Fragmentation subheader format

Syntax

Size

Notes

 

 

 

Fragmentation subheader () {

 

 

 

 

 

FC

2 bits

 

 

 

 

FSN

3 bits

 

 

 

 

reserved for CS use

3 bits

 

 

 

 

}

 

 

 

 

 

Copyright © 2002 IEEE. All rights reserved.

41

IEEE Std 802.16-2001

LOCAL AND METROPOLITAN AREA NETWORKS—PART 16:

The fields of the Fragmentation subheader are defined in Table 8.

 

 

 

Table 8—Fragmentation subheader fields

 

 

 

 

Name

Length

 

Description

(bits)

 

 

 

 

 

 

 

 

 

Fragmentation Control

 

 

Indicates the fragmentation state of the payload:

FC

2

00

= no fragmentation

01

= last fragment

 

 

 

 

10

= first fragment

 

 

11 = continuing (middle) fragment

 

 

 

 

 

Fragmentation Sequence Number

FSN

3

Defines the sequence number of the current SDU fragment. This field increments by one

 

 

(modulo 8) for each fragment, including unfragmented SDUs.

 

 

 

 

6.2.2.2.2 Grant Management subheader

The Grant Management (GM) subheader is two bytes in length and is used by the SS to convey bandwidth management needs to the BS. This subheader is encoded differently based upon the type of uplink scheduling service for the connection (as given by the CID). The use of this subheader is defined in 6.2.6. The Grant Management subheader is shown in Table 9. Its fields are defined in Table 10.

Table 9—Grant Management subheader format

Syntax

Size

Notes

 

 

 

Grant Management subheader() {

 

 

 

 

 

if (scheduling service type == UGS) {

 

 

 

 

 

SI

1 bit

 

 

 

 

PM

1 bit

 

 

 

 

reserved

14 bits

Set to 0

 

 

 

}

 

 

 

 

 

else {

 

 

 

 

 

PiggyBack Request

16 bits

 

 

 

 

}

 

 

 

 

 

}

 

 

 

 

 

42

Copyright © 2002 IEEE. All rights reserved.

AIR INTERFACE FOR FIXED BROADBAND WIRELESS ACCESS SYSTEMS IEEE Std 802.16-2001

 

 

 

Table 10—Grant Management subheader fields

 

 

 

 

Name

Length

 

Description

(bits)

 

 

 

 

 

 

 

 

 

PiggyBack Request

PBR

16

The number of bytes of uplink bandwidth requested by the SS. The bandwidth request is for

 

 

the CID. The request shall not include any PHY overhead.

 

 

 

 

 

Poll-Me

PM

1

0

= No action

 

 

1

= Used by the SS to request a bandwidth poll.

 

 

 

 

 

Slip Indicator

SI

1

0

= No action

 

 

1

= Used by the SS to indicate a slip of uplink grants relative to the uplink queue depth.

 

 

 

 

6.2.2.2.3 Packing subheader

When Packing (see 6.2.3.4) is used, the MAC may pack multiple SDUs into a single MAC PDU. When packing variable-length MAC SDUs, the MAC precedes each one with a Packing subheader. The Packing subheader is defined in Table 11.

Table 11—Packing subheader format

Syntax

Size

Notes

 

 

 

Packing sub-header () {

 

 

 

 

 

FC

2 bits

 

 

 

 

FSN

3 bits

 

 

 

 

Length

11 bits

 

}

The fields of the packing subheader are defined in Table 12.

 

 

Table 12—Packing subheader fields

 

 

 

Name

Length

Description

(bits)

 

 

 

 

 

 

 

Fragmentation Control

 

 

Indicates the fragmentation state of the payload:

FC

2

00 = no fragmentation

01 = last fragment

 

 

 

 

10 = first fragment

 

 

11 = continuing (middle) fragment

 

 

 

 

 

Fragmentation Sequence Number

FSN

3

Defines the sequence number of the current SDU fragment. This field increments by one

 

 

(modulo 8) for each fragment, including unfragmented SDUs.

 

 

 

Length

11

The length in bytes of the MAC SDU or SDU fragment, including the two-byte packing

subheader.

 

 

 

 

 

Copyright © 2002 IEEE. All rights reserved.

43

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