Shamir Stein Ackerman Elad Lifshitz Timor Israeli IEEE 802.16 WiMAX Shamir Stein Ackerman Elad Lifshitz Timor Israeli

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

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

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)

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.

802.16 Protocol stack Upper-layer architecture & interface specifications are out of the scope of 802.16

WiMax Physical Layer

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

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 802.16.e there are 4 types of modulation constellations: BPSK,QPSK, 16 QAM and 64 QAM

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

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

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 00 11 01 11 00 01 10 11 00 01 01 10 00 11 CP CP 1023 50 102.8

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

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)

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…..

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

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

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

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

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

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

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)