1. Shamir Stein Ackerman Elad Lifshitz Timor Israeli
IEEE WiMAX
Shamir Stein Ackerman
Elad Lifshitz
Timor Israeli

2. Outline Why Mobile WiMax over existing Wi-Fi? 802.16 standard history
Physical Layer
Transmit Power Control (TPC) In Uplink WiMax

3. What Is Mobile WiMax? Secure Broadband Wireless Fully Mobile IP based
Licensed spectrum
Cell based (Cellular)
High spectral efficiency

4. Why Mobile WiMax?
Mobile WiMax can take advantage of licensed spectrum owned by wireless service providers (instead of Wi-Fi unlicensed spectrum)
WiMax is a scheduled protocol, therefore no need for contention based protocols (like Wi-Fi CSMA/CA – less interference)
Rich Internet experience anywhere within a wide coverage range using antennas on towers with greater power levels than Wi-Fi networks, creating a network base on cellular ideas (instead of Wi-Fi hotspots)
Better tolerance to multipath propagation (OFDMA signals)

5. 802.16 Standards History Fixed access Data focused
Fixed and Portable access
Data, some Voice
Mobile access
Data, Audio, Voice, Video
Client integration for PC’s and Handhelds.

6. Protocol stack
Upper-layer architecture & interface specifications are out of the scope of

7. WiMax Physical Layer

8. OFDM OFDM: orthogonal frequency division multiplexing
Available bandwidth is divided into N orthogonal sub carriers
Each sub carrier individually modulated (QAM) at 1/N total data rate
FFT implementation (fast and efficient)
OFDM provides inherent resistance to multipath
Each sub carrier is narrowband and incurs flat fading
Low data rate per sub carrier cause low ISI
Use of cycle prefix guard interval ( with GI > delay spread) eliminates ISI while keeping sub carriers orthogonality

9. Sub Carrier Modulation
Modulating data using sine functions ( each sine in OFDM symbol represent one sub carrier which is also called tone)
Constellation view of a sine constructs of the amplitude and phase characteristics (exclude the frequency dimension).
In e there are 4 types of modulation constellations: BPSK,QPSK, 16 QAM and 64 QAM

10. Sub Carrier Modulation
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

11. BW and FFT – How it works Rx - Perform FFT Tx - Perform IFFT 00 01 1011
Rx - Perform FFT
Tx - Perform IFFT
FFT Size – 1024/512 Q I 1 -1 1 1 -1 -1 …
1023
BW – 10/5Mhz

12. 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)
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
1023 50
102.8

13. OFDMA OFDMA- orthogonal frequency division multiple access
Users are scheduled across both frequency (sub channels axis) and time (symbols axis)
Higher granularity in resource allocation
More degrees of freedom in scheduling

14. OFDMA: OFDM VS. OFDMA scheduling
OFDM gains multiple access by sharing in time ( one dimensional multiple access – time)
In OFDMA multiple access is 2 dimensional (time and frequency)

15. OFDMA advantages
Robust against frequency selective fading (OFDM symbol)
Robust against multipath and ISI (OFDM symbols)
Multi user access and efficient scheduling (orthogonality of UL users)
Users assigned modulation and coding according as a function of SINR
Users concentrate transmit power over partial BW
Ability to implement advanced MIMO techniques
and much more…..

16. OFDMA Subchannels
A subset of subcarriers is grouped together to form a subchannel
Subscriber may be assigned one or more sub channels , several users may transmit simultaneously

17. Time Division Duplexing (TDD)
DL and UL share the same RF channel
Subscriber do not transmit/receive simultaneously

18. 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)
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

19. 802.16 2D world – FRAMES More deeply view:
DL-MAP and UL-MAP indicate the frame structure

20. 802.16e 2D World – Zones & Permutations
Zones differ one from another in the way they convert the logical frequency (subchannels), into real frequency (sub carriers). The mathematics manipulation that does this conversion is called “permutation”
Each sub-frame can potentially be divided into zones (there’s at least one zone in each sub-frame)
1023

21. 802.16e World – Downlink Bursts
Bursts are the 2D objects, in which a BS modulate data to its mobile subscribers
properties:
“X” – OFDMA Symbol Offset
“Y” – Subchannel Offset
“U” – Number of OFDMA symbols
“V” - Number of Subchannels
FEC Type, FEC Rate, Repetition
CTC QPSK 1/2
Repetition - 6
CC QAM 64 5/6
Repetition - 1

22. Uplink – Transmission bursts
Uplink consists of control regions (“rectangles”), and data bursts (“snakes”):
Bursts – has the “snake” shape (“time first”):
saves bits of description in UL map.
Transmit Power advantages (compare to “frequency first” snake shapes)