C80216m-08_216

Project IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>

Title Downlink Physical Resource Allocation Unit

Date Submitted 2008-03-10

Source(s) Sean McBeath, JueJun Liu, Jianmin LuHuawei

E-mail: smcbeath@huawei.com

Re: IEEE 802.16m-08/005: Call for Contributions on Project 802.16m System Description Document (SDD).

Target topic: “Downlink Physical Resource Allocation Unit”.

Abstract Proposal for downlink physical resource allocation unit

Purpose For discussion and approval by TGm

Notice This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein.

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Introduction• The basic resource allocation block is a fundamental

design consideration for OFDMA systems• The size of the basic resource allocation block impacts

the following:– Capacity

• If the resource block is too large, the capacity for applications such as VoIP will be limited

– Assignment Message Overhead• If the resource block is too small, there will be unnecessary

overhead in the assignment messages– Control Signal Overhead

• Depending on the design, the number of resource blocks may be related to the number of resources needed for the acknowledgment channel

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VoIP Consideration• For VoIP, it is desirable for an integer number of

resource blocks for QPSK to have an approximate effective coding rate of 1/2– A spectral efficiency of 1 is the most common in system

simulations

• While the evaluation methodology uses the AMR vocoder, we should design the system to effectively support EVRC as well AMR

• We should consider a reduced MAC header when analyzing the basic resource allocation block size

AMR EVRCPayload 33 22RTP/UDP/IP 3 3MAC Header 3 3CRC 2 2Total 41 30

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QPSK Effective Coding Rate

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

60 92 124 156 188 220 252 284 316 348 380 412 444 476 508 540 572 604 636

Symbols * Subcarriers (Traffic)

1st H

AR

Q T

rans

mis

sion

Cod

ing

Rat

e

AMR QPSK

EVRC QPSK

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QPSK Effective Coding Rate

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

188 220 252 284 316 348 380 412

Symbols * Subcarriers (Traffic)

1st H

AR

Q T

rans

mis

sion

Cod

ing

Rat

e

AMR QPSK

EVRC QPSK

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Number of Subcarriers

Number of OFDM Symbols

1 2 3 4 5 612 6 58 115 173 230 288 34618 6 86 173 259 346 432 51824 6 115 230 346 461 576 691

Number of Resource Blocks

Conclusion• For VoIP, the number of traffic symbols times subcarriers in

an integer number of resource blocks should be between 220 and 348– For 6 OFDM symbol mini-frames, assuming 20% overhead for pilot

and control, the following table represents the number of traffic symbols times subcarriers for various number of resource blocks.

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Number of Subcarriers

Number of OFDM Symbols

1 2 3 4 5 612 6 0.95 0.71 0.57 0.4718 6 0.95 0.63 0.47 0.38 0.3224 6 0.71 0.47 0.36 0.28 0.24

Number of Resource Blocks

Conclusion– Recommendation: 12x6 or 18x6– The tables below show the effective coding rate for the first

HARQ transmission assuming 20% of the resource block is used for pilot and control (QPSK)

Number of Subcarriers

Number of OFDM Symbols

1 2 3 4 5 612 6 0.69 0.52 0.42 0.3518 6 0.69 0.46 0.35 0.28 0.2324 6 0.52 0.35 0.26 0.21 0.17

Number of Resource Blocks

AMR

EVRC

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Proposed Text

Insert the following text into Physical Layer sub-clause (IEEE C802.16m-08/003):

------------------------------- Text Start ---------------------------------------------------

11.1 Downlink Physical Resource Allocation Unit

The downlink physical resource allocation unit shall be 12 subcarriers by 6 OFDM symbols or 18 subcarriers by 6 OFDM symbols.

------------------------------- Text End ---------------------------------------------------