1. 802.16e PHY Basic concepts
By Timor Israeli

2. Modulating data using sine function
Sine functions characteristics enable modulation of bits
Characteristics :
Amplitude (power)
Phase
Cycle duration (Frequency)

3. Modulating data using sine function
Constellation view of a sine constructs of the amplitude and phase characteristics (exclude the frequency dimension).
Amplitude
Phase

4. Modulating data using sine function
In e there are 4 types of modulation constellations:
BPSK (For preamble, pilots and CDMA)
QPSK (Data, FFB)
QAM16 (Data)
QAM64 (Data)

5. Modulating data using sine function
The higher the SNR (CINR), the higher the QAM we can use (Link adaptation process chooses the best QAM)
Reduce to QAM4
SNR Fits QAM16
SNR Decreases

6. Rx Tx Bandwidth and FFT Power Frequency Modem - BB Modem - IF
“Bandwidth” is a consecutive region in the spectrum of frequencies, that is used to modulate data.
The modem is responsible for base band frequencies (up to 10 MHz), while the RF unit deals with RF frequencies (2-5 GHz) Rx Tx
Power
Frequency
Modem - BB
Modem - IF
RFIC - RF

7. Bandwidth and FFT In 802.16e there are 3 optional physical layers:
Single Carrier – One carrier (sine) occupies the entire energy over the bandwidth
Multi Carrier – OFDM (Orthogonal Frequency Division Multiplexing)
Multi Carrier – OFDMA (Orthogonal Frequency Division Multiplexing Access)

8. Rx - Perform FFT Tx - Perform IFFT BW and FFT – How it works 00 01 1011
Rx - Perform FFT
Tx - Perform IFFT
FFT Size – 1024/512 Q I 1 -1 1 1 -1 -1 …

9. CP, BW, FFT size and OFDM Symbol
OFDM symbol, is the duration of one context of the FFT (i.e. – before the modulator (BS/MS) encode different bits to the same tones)
Cyclic Prefix is a repetition in time of 1/8 of the OFDM symbol. It is used to overcome symbol interferences (inter/intra), and also helps to detect WiMax transmissions (periodicity of the PREAMBLE)
Symbol duration is derived by CP ratio (1/8), the FFT size and the BW (equals to ~(FFT/BW)*(1+CP_RATIO) )
Symbol 1 CP CP 50
102.8

10. 802.16e 2D World - Frames TTG RTG
2D world constructs of a time axis (symbol axis) and frequency axis (subchannels axis)
A frame is a duration of 5 milliseconds. Each frame is divided into two sub-frames : Downlink and Uplink (DL/UL)
Each sub-frame can potentially be divided into zones (there’s at least one zone in each sub-frame)
A WiMax transmission is constructed from an endless sequence of frames.
Note that DL and UL are separated by TTG and RTG durations
TTG
RTG

11. 802.16e 2D World – Zones & Permutations
Zones differ one from another in the way they convert the logical frequency (subchannels), into real frequency (subcarriers). The mathematics manipulation that does this conversion is called “permutation” DL
# SubCh / # Slot Duration
Perm\FFT
1024
512
PUSC
30 / 2
15 / 2
FUSC
16 / 1
8 / 1
AMC
48 / 3
24 / 3 UL
# SubCh / # Slot Duration
Perm\FFT
1024
512
PUSC
35 / 3
17 / 3
AMC
48 / 3
24 / 3
1023

12. 802.16e World - Downlink PUSC
The division to groups of subchannels, allow division to geographical division of sectors.
The DL always begins with PUSC (Partial Usage SubChannelization). This means that at least the two symbols following the PREAMBLE are part of the PUSC zone.
In PUSC, the subchannels are divided into major and mimor groups (e.g. for 1024 FFT, group 0 is constructed by subchannels 0-5, group 1 is constructed by subchannels 6-9, group 2 by subchannels 10-15, and so on up to group 5).
Major
Minor

13. 802.16e World – Downlink Bursts
Bursts are the 2D objects, in which a BS modulate data to its mobile subscribers (MSs)
properties:
“X” – OFDMA Symbol Offset
“Y” – Subchannel Offset
“U” – Number of OFDMA symbols
“V” - Number of Subchannels
FEC Type, FEC Rate, Repetition
Boosting
Burst’s size 
CTC QPSK 1/2
Repetition - 6
CC QAM 64 5/6
Repetition - 1
number_of_slots * 48 * log2(QAM) * rate / repetition
PUSC Example  (6/2*24) * 48 * 2 * 1/2 / 6 = 576 bits = 72 bytes
FUSC Example  (2*13) * 48 * 6 * 5/6 / 1 = 6240 bits = 780 bytes

14. 802.16e World – Uplink Bursts & Controls
Uplink consists of control regions (“rectangles”), and data/harq bursts (“snakes”):
CDMA IR/HO; PER/BWR – contention based regions. Used in ranging processes, as well as for BW request.
FFB – Fast Feedback region. Used for fast CINR/RSSI report (MS to BS)
HARQ Ack/Nack – used to Ack/Nack HARQ transmissions on the DL sub frame
Bursts – has the “snake” shape – saves bits of description in UL map.

15. 802.16e World – Normal Maps
Maps are MAC messages that come in a special DL bursts. The Maps describe the 2D characteristics of the frame.
DL MAP describes the bursts over the DL sub frame. It has a frequency-first “snake” shape, and always start at symbol 1, subchannel 4
UL Map describes the bursts and control regions over the next UL sub-frame. It is the first PDU in the first data burst.
FCH – The first burst in the DL. Describes the DL Map that follows it.

16. 802.16e World – Compressed & Sub Maps
Motivation – save in BW of maps 
Combine the DL and UL into one map, and thus save headers
Divide the maps to MCSs (QAM) and fit to each MS a map according its SNR