6.5 Burst Profile


6.5 Burst Profile

The burst profile is a basic tool in the 802.16 standard MAC Layer. The burst profile allocation, which changes dynamically and possibly very fast, is about physical transmission. Here the parameters of the burst profiles of WiMAX are summarised. The burst profiles are used for the link adaptation procedure. The use of burst profiles and the link adaptation procedure will be seen in more detail in Chapters 9 and 10.

6.5.1 Downlink Burst Profile Parameters

The burst profile parameters of a downlink transmission for OFDM and OFDMA PHYsical layers are proposed in Table 6.2. The parameter called FEC code is in fact the Modulation and Coding Scheme (MCS). For OFDM PHY, there are 20 MCS combinations of modulation (BPSK, QPSK, 16-QAM or 64-QAM), coding (CC, RS-CC, CTC or BTC) and coding rate (1/2, 2/3, 3/4 and 5/6). The most frequency-use efficient (and then less robust) MCS is 64-QAM (BTC) 5/6. For OFDMA PHY, there are 34 MCS combinations of modulation (BPSK, QPSK, 16-QAM or 64-QAM), coding (CC, ZT CC, CTC, BTC, CC with optional interleaver) and coding rate (1/2, 2/3, 3/4 and 5/6). The Downlink Interval Usage Code (DIUC) is the burst usage descriptor (see Chapter 9), which includes the burst profile.

Table 6.2: Downlink burst profile parameters for OFDM and OFDMA PHYsical layers
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Burst profile parameter

Description

Frequency (in kHz)

Downlink frequency

FEC code type

Modulation and Coding Scheme (MCS); there are 20 MCSs in OFDM PHY and 34 MCSs in OFDMA PHY (as updated in 802.16e)

DIUC mandatory exit threshold

The CINR at or below where this burst profile can no longer be used and where a change to a more robust (but also less frequency-use efficient) burst profile is required. Expressed in 0.25 dB units. See Chapter 9 for DIUC

DIUC minimum entry threshold

The minimum CINR required to start using this burst profile when changing from a more robust burst profile. Expressed in 0.25 dB units

TCS_enable (OFDM PHY only)

Enables or disables TCS

6.5.2 Uplink Burst Profile Parameters

The burst profile parameters of an uplink transmission for an OFDM PHY and an OFDMA PHY are proposed in Tables 6.3 and 6.4 respectively.

Table 6.3: Uplink burst profile parameters for the OFDMA PHYsical Layer
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Burst profile parameter

Description

FEC type and modulation type

There are 20 MCSs in OFDM PHY

Focused contention power boost

The power boost in dB of focused contention carriers (see Chapter 10)

TCS_enable

Enables or disables TCS

Table 6.4: Uplink burst profile parameters for the OFDMA PHYsical Layer
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Burst profile parameter

Description

FEC type and modulation type

There are 52 MCSs in OFDMA PHY

Ranging data ratio

Reducing factor, in units of 1 dB, between the power used for this burst and the power used for CDMA ranging (see Chapter 11); encoded as a signed integer

6.5.3 MCS Link Adaptation

The choice between different burst profiles or, equivalently, between different MCSs is a powerful tool. Specifically, choosing the MCS most suitable for the state of the radio channel, at each instant, leads to an optimal (highest) average data rate. This is the so-called link adaptation procedure. In the following chapters the MAC procedures that can be used for the implementation of link adaptation are described. The link adaptation algorithm in itself is not indicated in the 802.16 standard. It is left to the vendor or operator.

The order of magnitudes of SNR thresholds can be obtained from Table 6.5, proposed in the standard [1] for some test conditions. These SNR thresholds are for a BER, Bit-Error Rate, measured after the FEC, that is smaller than 10−6.

Table 6.5: Received SNR threshold assumptions [1], Table 266. (From IEEE Std 802.16-2004 [1]. Copyright IEEE 2004, IEEE. All rights reserved.)
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Modulation

Coding rate

Receiver SNR threshold (dB)

BPSK

1/2

6.4

QPSK

1/2

9.4

QPSK

3/4

11.2

QAM-16

1/2

16.4

QAM-16

3/4

18.2

QAM-64

1/2

22.7

QAM-64

3/4

24.4




WiMAX. Technology for Broadband Wireless Access
WiMAX: Technology for Broadband Wireless Access
ISBN: 0470028084
EAN: 2147483647
Year: 2007
Pages: 124

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