WiMAX 1EEE 802.16 Protocol Stack Lecture-2 Presented By Laiq Akhtar

Scope of 802 standards

WiMAX 1EEE 802.16 Protocol Stack General Structure Similar to other IEEE 802 networks But with more sub layers. Higher Layers Protocols (3& above )are independent of Network Architecture & Applicable to a variety of networks . Focused on the lowest two layers Protocols defined specifically for wireless transmission address issues related to transmission of data over the network

WiMAX 1EEE 802.16 Protocol Stack

WiMAX 1EEE 802.16 Protocol Stack

Protocol Architecture Physical and transmission layer functions: Modulation & Demodulation Of signal Encoding/decoding of signals Bit transmission/reception Power Management Multiple PHY Layers & Services for the freq bands of the application . Applicable to system operating between 10 and 66 GHz.

Multiplexing Technology :OFDM WiMAX uses OFDM, a multicarrier technique that allows broadband transmission in a mobile environment with fewer multi-path effects than a single signal with broad bandwidth modulation. The WiMAX physical layer is based on orthogonal frequency division multiplexing. Multicarrier modulation uses multiple carrier signals at different frequencies sending some of bits on each channel. Similar to FDM.

PHY Layer OFDM

PHY Layer OFDM

802.16a PHY Layer Features: 256-point FFT OFDM waveform :Built-in support for addressing multi-path in outdoor LOS and NLOS environments Adaptive modulation :Ensures a robust RF link while maximizing the number of bits/ second for each subscriber unit TDD and FDD duplexing support: Addresses varying worldwide regulations where one or both may be allowed

IEEE802.16a PHY Layer Features Flexible channel sizes (e.g., 3.5 MHz, 5 MHz, 10 MHz, etc.) :Provides the flexibility necessary to operate in many different frequency bands with varying channel requirements around the world Designed to support smart antenna systems Smart antennas are fast becoming more affordable, and as these costs come down their ability to suppress interference and increase system gain will become

The modulation is one of the four digital modulations BPSK, QPSK, 16-QAM or 64-QAM. The modulated symbols are then transmitted on the OFDM orthogonal subcarriers.

Binary Phase Shift Keying (BPSK) The BPSK is a binary digital modulation; i.e. one modulation symbol is one bit. This gives high immunity against noise and interference and a very robust modulation. A digital phase modulation, which is the case for BPSK modulation, uses phase variation to encode bits: each modulation symbol is equivalent to one phase. The phase of the BPSK modulated signal is π or -−π according to the value of the data bit

Quadrature Phase Shift Keying (QPSK) When a higher spectral efficiency modulation is needed, i.e. more b/s/Hz, greater modulation symbols can be used. For example, QPSK considers two-bit modulation symbols. The QPSK modulation is therefore less noiseresistant than BPSK as it has a smaller immunity against interference. A well-known digital communication principle must be kept in mind: ‘A greater data symbol modulation is more spectrum efficient but also less robust.’

Quadrature Amplitude Modulation (QAM): 16-QAM and 64-QAM 64QAM provides high throughput at sub maximum range, whereas lower-order modulation(e.g., 16QAM) provides lower throughput at higher range, from the same base station.

Adaptive Modulation

Adaptive Modulation

Illustration of link adaptation Illustration of link adaptation. A good radio channel corresponds to a high-efficiency Modulation and Coding Scheme (MCS)

Adaptive Modulation Having more than one modulation has a great advantage: link adaptation can be used (this process is also used in almost all other recent communication systems such as GSM/EDGE, UMTS, WiFi, etc.). The principle is rather simple: when the radio link is good, use a high-level modulation; when the radio link is bad, use a low-level, but also robust, modulation. radio channel is better when an SS is close to the BS. Another dimension is added to this figure when the coding rate is also changed

Duplexing Technology Duplexing refers to the process of creating bidirectional channels for uplink and downlink data transmission. TDD and FDD are both supported by the 802.16-2004 standards. FDD, unlike TDD, requires two channel pairs that are separated to minimize interference, one for transmission and the other for reception. Most FDD bands are allocated to voice, because the bidirectional architecture of FDD allows voice to be handled with minimal delays

Duplexing Technology FDD, however, adds additional components to the system and therefore increases costs. FDD is also used in 3G networks, which operate at a known frequency and are designed for voice applications. TDD is more efficient for IP or data.

Flexible Channel Bandwidth As the distance between a subscriber and the base station increases, or as the subscriber starts to move by walking or driving in a car, it becomes more of a challenge for him or her to transmit successfully back to the base station at a given power level. For power-sensitive platforms such as laptop computers or handheld devices, it is often not possible for them to transmit to the base station over long distances if the channel bandwidth is wide.

Flexible Channel Bandwidth Unlike 802.11 (fixed 20 MHz channel bandwidth) and 3G (limited channel bandwidth of 1.5 MHz), IEEE 802.16-2004 and IEEE 802.16e standards have flexible channel bandwidths between 1.5 and 20 MHz to facilitate transmission over longer ranges and to different types of subscriber platforms. In addition, this flexibility of channel bandwidth is also crucial for cell planning, especially in the licensed spectrum.

Power Control In any WiMAX network, power levels and control for both transmit and receive are important for system efficiency. Power-control algorithms are used Power control reduces the overall power consumption of the CPE and the potential interference with other co-located base stations.

Power Control Power levels are dynamically adjusted on a per-subscriber basis, depending on the profile and distance from the base station. For the base station transmitter, the actual transmitted power will depend on the subscriber distance, propagation characteristics, channel bandwidth, and modulation scheme (BPSK, QPSK, 16QAM, or 64QAM).

Power Control The least data-efficient method is BPSK. Because it is employed where the subscriber station is farthest from the base, BPSK requires additional transmit power. 64QAM offers high data efficiency, which is best when the subscriber station is closer to the base station.

Physical Layer – Upstream Transmission Uses a DAMA-TDMA technique Error correction uses Reed-Solomon code Modulation scheme based on QPSK

Physical Layer – Downstream Transmission Continuous downstream mode For continuous transmission stream (audio, video) Simple TDM scheme is used for channel access Duplexing technique is frequency division duplex (FDD) Burst downstream mode Targets burst transmission stream (IP-based traffic) DAMA-TDMA scheme is used for channel access Duplexing techniques are FDD with adaptive modulation, frequency shift division duplexing (FSDD), time division duplexing (TDD)