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   Padder, 802.11a (PAD11A)       

Padder, 802.11a (PAD11A)

Limits

Notes

1. This model can be used to form DATA field bits by prepending the SERVICE field, add tail bits and pad bits, according to IEEE 802.11a standard.

2. Fig.1 shows the format for the PPDU including the OFDM PLCP preamble, OFDM PLCP header, PSDU, tail bits, and pad bits. The PLCP header contains the following fields: LENGTH, RATE, a reserved bit, an even parity bit, and the SERVICE field. In terms of mod­ulation, the LENGTH, RATE, reserved bit, and parity bit (with 6 “zero” tail bits appended) constitute a separate single OFDM symbol, denoted SIGNAL, which is transmitted with the most robust combination of BPSK modulation and a coding rate of R=1/2. The SERVICE field of the PLCP header and the PSDU (with 6 “zero” tail bits and pad bits appended), denoted as DATA, are transmitted at the data rate described in the RATE field and may constitute multi­ple OFDM symbols. The tail bits in the SIGNAL symbol enable decoding of the RATE and LENGTH fields immediately after the reception of the tail bits. The RATE and LENGTH are required for decoding the DATA part of the packet. We will describe the DATA field in the following sections

Fig.1 PPDU frame format

3. Service field (SERVICE)
The IEEE 802.11 SERVICE field has 16 bits, which shall be denoted as bits 0~15, as shown in Fig.2. The bit 0 shall be transmitted first in time. The bits from 0~6 of the SERVICE field, which are transmitted first, are set to zeros and are used to synchronize the descrambler in the receiver. The remaining 9 bits (7~15) of the SERVICE field shall be reserved for future use. All reserved bits shall be set to zero.

Fig.2 SERVICE field bit assignment

4. Tail bits field (TAIL)
The PPDU tail bits field shall be six bits of “0”, which are required to return the convolutional encoder to the “zero state”. This procedure improves the error probability of the convolutional decoder, which relies on future bits when decoding and which may be not be available past the end of the message. The PLCP tail bit field shall be produced by replacing six scrambled “zero” bits following the message end with six nonscrambled “zero” bits.

5. Pad bits (PAD)
The number of bits in the DATA field shall be a multiple of N_CBPS, the number of coded bits in an OFDM symbol (48, 96, 192, or 288 bits), as shown in Table I. To achieve that, the length of the message is extended so that it becomes a multiple of N_DBPS, the number of data bits per OFDM symbol. N_CBPS and N_DBPS can be determined by the two parameters, Modulation and Coding as shown in Table I. At least 6 bits are appended to the message, in order to accommo­date the TAIL bits. The number of OFDM symbols N_SYM the number of bits in the DATA field N_DATA and the number of pad bits N_PAD are computed from the length of the PSDU (Length) as follows:

(1)

(2)

(3)
The function ceiling (.) is a function that returns the smallest integer value greater than or equal to its argument value. The appended bits (“pad bits”) are set to “zeros” and are subsequently scrambled with the rest of the bits in the DATA field.

Table I IEEE 802.11a Rate-dependent parameter

Netlist Form

PAD11A:NAME n1 n2 [MODULATION =val] [CODING =val]
+ [LENGTH =val] [RIN=val] [ROUT=val]

Netlist Example

PAD11A:1 1 2 MODULATION = 2 CODING= 2 LENGTH = 100

References

1. IEEE Std 802.11a, Part 11: “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band,” ISO/IEC 8802-11:1999/Amd 1:2000(E).

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