802.16e PHY Basic concepts By Timor Israeli

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

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

Modulating data using sine function In 802.16e there are 4 types of modulation constellations: BPSK (For preamble, pilots and CDMA) QPSK (Data, FFB) QAM16 (Data) QAM64 (Data)

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

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

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)

Rx - Perform FFT Tx - Perform IFFT BW and FFT – How it works 00 01 10 11 Rx - Perform FFT Tx - Perform IFFT FFT Size – 1024/512 Q I 1 -1 1 1 -1 -1 …

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 00 11 01 11 00 01 10 11 00 01 01 10 00 11 CP CP 50 102.8

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

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

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

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

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.

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.

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