WiMAX Vs Wi-Fi. 3G Evolution (source: Nokia) Wireless Systems. WiMAX

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1 3G Evolution (source: Nokia) WiMAX Vs Wi-Fi ผศ.ดร.ส ร นทร ก ตต ธรก ล ภาคว ชาว ศวกรรมคอมพ วเตอร คณะว ศวกรรมศาสตร สถาบ นเทคโนโลย พระจอมเกล าเจ าค ณทหารลาดกระบ ง 2 Wireless Systems WiMAX Worldwide Interoperability for Microwave Access Brand licensed by the WiMax Forum. a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL WiMAX was seen as more of a Metropolitan Area Network (MAN) technology providing a much larger coverage. Based on IEEE

2 IEEE Introduction Source: WiMAX, making ubiquitous high-speed data services a reality, White Paper, Alcatel. Migration of WiMAX Data Rate Fixed WiMAX IEEE d 2005 SOC Available Portable WiMAX Nomadic WiMAX IEEE d/e 2006? Standard Maturing Standard Maturing Mobile WiMAX IEEE e 2007? Mobility WiMAX WiMAX, in fact, comes in two forms, a so called fixed WiMAX and a mobile WiMAX. WiMAX in its fixed form is seen as a possible alternative to expensive cable and fibre deployment. It is faster to deploy and less expensive and it also offers operators more flexibility in terms of deployment time frame and possible installation areas. 3G or other cellular network operators could see this as a potential substitute or as a complement to their cellular product. 8

3 Network Architecture Channel Characteristics GHz Very weak multipath components (LOS is required) Rain attenuation is a major issue Single-carrier PHY 2-11 GHz Multipath NLOS Single and multi-carrier PHYs Advantages in Multipath A carries advantages in Multipath CDMA uses the whole spectrum, wasting system resource to combat frequency selective fading. CDMA also creates worse interference problem A only select subcarriers with less channel degradation, prevent wasting system resource (power or throughput ) => achieving higher system capacity. Multipath Signal Sent Signal Received

4 Physical Layer Summary A Scalability Designation Applicability MAC Duplexing WirelessMAN-SC GHz Licensed Basic TDD, FDD, HFDD WirelessMAN-SC 2-11 GHz Licensed Basic, (ARQ), (STC), (AAS) TDD, FDD 2-11 GHz Licensed Basic, (ARQ), (STC), (AAS) TDD, FDD WirelessMAN GHz Licenseexempt Basic, (ARQ), (STC), (DFS), (MSH), (AAS) TDD 2-11 GHz Licensed Basic, (ARQ), (STC), (AAS) TDD, FDD WirelessMAN-A 2-11 GHz Licenseexempt Basic, (ARQ), (STC), (DFS), (MSH), (AAS) TDD Supports s wide range of frame sizes (2-20 ms) Source: Intel Scalable A Physical Layer in IEEE WirelessMAN Adaptive PHY Spectral Efficiency Wins Spectrum efficiency is an important factor for data service The scarce of available (or useful) spectrum makes efficiency a key factor to approve spectrum and the success of business model. Regulatory bodies shall recycle spectrum for existing systems with low spectral efficiency. Future systems with high spectrum re-use advantages or higher spectral efficiency shall have favored allocation during application. 2.5G TDMA: Very limited data rate and low spectral efficiency ( bps/hz) 3G WCDMA: Reasonable data rate, range, and mobility, improved spectral efficiency ( bps/hz) Source: Understanding WiMAX and 3G for Portable/Mobile Broadband Wireless, Technical White Paper, Intel. WiFi: 64FFT, Reasonable data rate, limited range and mobility, improved spectral efficiency (2-3 bps/hz) 500kHz WiMAX:A, Up to 2048FFT much improved range and mobility, potential for best spectral efficiency (3-4 bps/hz) 5MHz 15 MHz 20 MHz

5 Reference Model Duplex Scheme Support The duplex scheme is Usually specified by regulatory bodies, e.g., FCC Time-Division Duplex (TDD) Downlink & Uplink time share the same RF channel Dynamic asymmetry does not transmit & receive simultaneously (low cost) Frequency-Division Duplex (FDD) Downlink & Uplink on separate RF channels Full Duplexing (FDX): can Tx and Rx simultaneously; Half-duplexing (HDX) SSs supported (low cost) IEEE MAC PHY FDD Frame Structure Time Division Duplexing (TDD) Time Frame n-1 Frame n Frame n+1 Subframe TDM TDMA pre. FCH burst 1 burst 2... burst k pre. burst k+1... pre. burst n Broadcast Control Msgs MAP UL DCD MAP opt. UCD opt. UL subframe UL MAP for next MAC frame UL bursts pre. UL burst 1 UL TDMA... pre. UL burst m

6 IEEE MAC PHY TDD Frame Structure Frame Structure Another View Time Frame n-1 Frame n Frame n+1 Adaptive Subframe UL subframe pre. FCH burst 1 TDM UL TDMA... burst n... pre. UL burst 1 pre. UL burst m burst 2 MAP UL MAP DCD opt. UCD opt. Broadcast Conrol msgs IEEE MAC Convergence Sub-Layer (CS) ATM Convergence Sub-Layer: Support for VP/VC switched connections Support for end-to-end signaling of dynamically created connections ATM header suppression Full QoS support Packet Convergence Sub-Layer: Initial support for Ethernet, VLAN, IPv4, and IPv6 Payload header suppression Full QoS support IEEE MAC -- CS Packet Convergence Sub-Layer Functions: Classification: mapping the higher layer PDUs (Protocol Data Units) into appropriate MAC connections Payload header suppression (optional) MAC SDU (Service Data Unit), i.e, CS PDU, formatting PHSI MAC SDU = CS PDU Payload Header Suppression Index Optional, Depending on upper layer protocol Packet PDU (e.g., IP packet, Ethernet Packet)

7 IEEE MAC -- CPS MAC PDU Format IEEE MAC -- CPS -- Three Types of MAC PDUs MAC PDU msb Generic MAC Header (6 bytes) Generic MAC Header Format (Header Type (HT) = 0) H T E C Type (6 bits) LEN lsb (8) CID lsb (8) rs v C I EKS (2) rs v CID msb (8) HCS (8) LEN msb (3) payload (optional) BW Req. Header Format (Header Type (HT) =1) H T E C Type (6 bits) BWS Req. lsb (8) CID lsb (8) BW Req. msb (8) lsb CRC (optional) CID msb (8) HCS (8) Data MAC PDUs HT = 0 Payloads are MAC SDUs/segments, i.e., data from upper layer (CS PDUs) Transmitted on data connections Management MAC PDUs HT =0 Payloads are MAC management messages or IP packets encapsulated in MAC CS PDUs Transmitted on management connections BW Req. MAC PDUs HT =1; and no payload, i.e., just a Header IEEE MAC -- CPS Data Packet Encapsulations -- MAC Management Connections Packet PDU (e.g., Ethernet) CS PDU (i.e., MAC SDU) MAC PDU HT P H SI Ethernet Packet Ethernet Packet MAC PDU Payload CRC Each SS has 3 management connections in each direction: Basic Connection: short and time-urgent MAC management messages MAC mgmt messages as MAC PDU payloads Primary Management connection: FEC FEC block 1 FEC Block 2 FEC Block 3 FEC block m longer and more delay tolerant MAC mgmt messages MAC mgmt messages as MAC PDU payloads Secondary Management Connection: PHY Burst (e.g., TDMA burst) Preamble 1 2 n Standard based mgmt messages, e.g., DHCP, SNMP, etc IP packets based CS PDU as MAC PDU payload

8 MAC Management Messages MAC mgmt message format: 8 bits mgmt msg HD MAC mgmt msg payload MAC mgmt msg can be sent on: Basic connections; Primary mgmt connection; Broadcast connection; and initial ranging connections 41 MAC mgmt msgs specified in The TLV (type/length/value) encoding scheme is used in MAC mgmt msg, e.g., in UCD msg for UL burst profiles, (type=1, length=1, value=1) QPSK modulation (type=1, length=1, value=2) 16QAM modulation (type=1, length=1, value=3) 64QAM modulation MAC PDU Transmission MAC PDUs are transmitted in PHY Bursts The PHY burst can contain multiple FEC blocks MAC PDUs may span FEC block boundaries Concatenation Packing Segmentation Sub-headers MAC PDU Concatenation Multiple MAC PDUs are concatenated into the same PHY burst MAC PDU Fragmentation A MAC SDU can be fragmented into multiple segments, each segment is encapsulated into one MAC PDU FEC HT MAC PDU 1 MAC PDU 2 MAC PDU Payload CRC HT MAC PDU Payload CRC FEC block 1 FEC Block 2 FEC Block 3 HT MAC PDU k MAC PDU Payload FEC block m CRC Fragmentation Sub-Header (8 bits) FEC HT F S H FEC block 1 MAC SDU seg-1 MAC PDU Payload CRC HT FEC Block m1 MAC SDU F S H MAC SDU seg-2 MAC PDU Payload CRC FEC block 1 MAC SDU seg-3 HT F S H MAC PDU Payload CRC FEC Block m2 PHY Burst (e.g., TDMA burst) Preamble 1 2 n Pre. 1 n1 Pre. 1 n2 PHY Burst PHY Burst

9 MAC PDU Packing QoS Packing with fixed size MAC SDUs (no packing sub-header is needed) HT MAC SDU 1 MAC SDU 2 MAC PDU Payload MAC SDU k CRC Fixed size MSDUs, e.g., ATM Cells, on the same connection Packing with variable size MAC SDUs (Packing Sub-Heade is neeeded) Packing Sub-Heder (16 bits) MAC SDU or seg. 1 MAC SDU or seg 2 MAC SDU or seg n Variable size MSDUs or MSDU segments, e.g., IP packets, on the same connection Three components of QoS Service flow QoS scheduling Dynamic service establishment Two-phase activation model (admit first, then activate) Service Flow A unidirectional MAC-layer transport service characterized by a set of QoS parameters, e.g., latency, jitter, and throughput assurances Identified by a 32-bit SFID (Service Flow ID) Three types of service flows Provisioned: controlled by network management system Admitted: the required resources reserved by BS, but not active Active: the required resources committed by the BS HT PSH PSH PSH CRC Uplink Service Classes Uplink Services: UGS UGS: Unsolicited Grant Services rtps: Real-time Polling Services nrtps: Non-real-time Polling Services BE: Best Effort UGS: Unsolicited Grant Services For CBR or CBR-like services, e.g., T1/E1. The BS scheduler offers fixed size UL BW grants on a real-time periodic basis. The SS does not need to send any explicit UL BW req.

10 Uplink Services: rtps rtps: Real-time Polling Services For rt-vbr-like services, e.g., MPEG video. The BS scheduler offers real-time, periodic, UL BW request opportunities. The SS uses the offered UL BW req. opportunity to specify the desired UL BW grant. The SS cannot use contention-based BW req. Uplink Services: nrtps nrtps: non-real-time polling services For nrt-vbr-like services, such as, bandwidthintensive file transfer. The BS scheduler shall provide timely (on a order of a second or less) UL BW request opportunities. The SS can use contention-based BW req. opportunities to send BW req. Uplink Services: BE BE: Best Effort For best-effort traffic, e.g., HTTP, SMTP. The SS uses the contention-based BW request opportunities. Bandwidth Grant BW grants are per Subscriber Station: Allows real-time reaction to QoS need, i.e., SS may re-distribute bandwidth among its connections, maintaining QoS and service-level agreements Lower overhead, i.e., less UL-MAP entries compare to grant per connection Off- loading base station s work Requires intelligent subscriber station to redistribute the allocated BW among connections

11 BW Request/Grant Mechanisms Implicit requests (UGS): No actual requests BW request messages, i.e., BW req. header Sends in either a contention-based BW req. slot or a regular UL allocation for the SS;he special B Requests up to 32 KB with a single message Request Incremental or aggregate, as indicated by MAC header Piggybacked request (for non-ugs services only) Presented in Grant Management (GM) sub-header in a data MAC PDU of the same UL connection is always incremental Up to 32 KB per request for the CID Poll-Me bit Presented in the GM sub-header on a UGS connection request a bandwidth req. opportunity for non-ugs services -- Contention UL Access Two types of Contention based UL slots Initial Ranging Used for new SS to join the system Requires a long preamble BW Request Used for sending BW req Short preamble Collision Detection and Resolution Detection: SS does not get the expected response in a given time Resolution: a truncated binary exponential backoff window UL Sub-Frame Structure Ranging Ranging is a process of acquiring the correct timing offset, and PHY parameters, such as, Tx power level, frequency offset, etc. so that the SS can communicate with the BS correctly. BS performs measurements and feedback. SS performs necessary adjustments. Two types of Ranging: Initial ranging: for a new SS to join the system Periodic ranging (also called maintenance ranging): dynamically maintain a good RF link. Source:

12 Automatic Repeat request (ARQ) A Layer-2 sliding-window based flow control mechanism. Per connection basis. Only effective to non-real-time applications. Uses a 11-bit sequence number field. Uses CRC-32 checksum of MAC PDU to check data errors. Maintain the same fragmentation structure for Retransmission. Optional. IEEE MAC Privacy Sub-layer (PS) Two Major Functions: Secures over-the-air transmissions Protects from theft of service Two component protocols: Data encryption protocol A client/server model based Key management protocol (Privacy Key Management, or PKM) IEEE MAC PS -- Security Associations A set of privacy information, e.g., encryption keys, used encryption algorithm Three types of Security Associations (SAs) Primary SA: established during initial registration Static SA: provisioned within the BS Dynamic SA: dynamically created on the fly Identified by a 16-bit SAID Connections are mapped to SAs IEEE MAC PS -- Multi-level Keys and Their Usage Public Key Contained in X.509 digital certificate Issued by SS manufacturers Used to encrypt AK Authorization Key (AK) Provided by BS to SS at authorization Used to derive KEK Key Encryption Key (KEK) Derived from AK Used to encrypt TEK Traffic Encryption Key (TEK) Provided by BS to SS at key exchange Used to encrypt traffic data payload

13 IEEE MAC PS -- Data Encryption Use DES (Data Encryption Standard) in CBC (Cipher Block Chaining) mode with IV (Initialization Vector). CBC IV is calculated from IV parameter in TEK keying info; and PHY synchronization field in -MAP. Only MAC PDU payload (including subheaders) is encrypted. MAC PDU headers are unencrypted. Management messages are unencrypted. Wi-Fi Stands for Wireless Fidelity. Brand licensed by the Wi-Fi Alliance. Wi-Fi is a local area network technology that was originally thought to replace the thousands of miles of LAN cables. Wireless Local Area Networks (WLAN) Based on IEEE Wi-Fi Wi-Fi has grown from being just a LAN cable replacement technology to a public wireless access technology. Cheap and readily available equipment. WiFi has been viewed as complementary to 3G and other mobile standards as it has worked to enhance mobile services offered by operators. It s coverage is not as great as that of 3G, but it gives a much higher transmission rate than mobile technology. Wi-Fi New developments are taking place within the standardization group With the increasing popularity of VoIP, many see WiFi as one of the possible means of using VoIP with some form of mobility r for wireless VoIP and other real time applications s for meshed WiFi networking Handoff between WiFi access points is still not possible and, therefore, it is known more as a wireless access technology than a mobile technology. 51 Making WiFi more mobile could make it more of a substitute to mobile technologies 52

14 Scalability Bit Rate: Relative Performance Channel Bandwidth Maximum Data Rate Maximum bps/hz a 20 MHz 54 Mbps ~2.7 bps/hz Wide, fixed (20MHz) frequency channels Channel bandwidths can be chosen by operator (e.g. for sectorization) 1.5 MHz to 20 MHz width channels. MAC designed for scalability independent of channel bandwidth 10, 20 MHz; a 1.75, 3.5, 7, 14 MHz; 63 Mbps* ~5.0 bps/hz 3, 6 MHz * Assuming a 14 MHz channel MAC designed to support 10 s of users MAC designed to support thousands of users a is designed for metropolitan performance Coverage Range Optimized for indoor performance No mesh topology support within ratified standards Optimized for outdoor NLOS performance Standard supports mesh network topology Standard supports advanced antenna techniques Optimized for ~100 meters No near-far compensation. Designed to handle indoor multipath(delay spread of 0.8μ seconds). Optimization centers around PHY and MAC layer for 100m range. Optimized for up to 50 Km Designed to handle many users spread out over kilometers Designed to tolerate greater multi-path delay spread (signal reflections) up to 10.0μ seconds PHY and MAC designed with multimile range in mind Range can be extended by cranking up the power but MAC may be non-standard. StandardMAC;Sectoring/MIMO/AMC for Rate/Range dynamic tradeoff is designed for market coverage is designed for distance 55 56

15 Quality of Service (QoS) Contention-based MAC (CSMA/CA) => no guaranteed QoS Standard cannot currently guarantee latency for Voice, Video Standard does not allow for differentiated levels of service on a per-user basis a Grant-request MAC Designed to support Voice and Video from ground up Supports differentiated service levels: e.g. T1 for business customers; best effort for residential. Security Existing standard is WPA + WEP i in process of addressing security a Triple-DES (128-bit) and RSA (1024-bit) TDD only asymmetric e (proposed) QoS is prioritization only TDD/FDD/HFDD symmetric or asymmetric Centrally-enforced QoS a is designed for carrier class operation a maintains fixed wireless security WiMAX vs Wi-Fi WiMAX vs Wi-Fi 59 60

16 Comparison of WiMAX, WiFi and 3G technology vs : Summary and both gain broader industry acceptance through conformance and interoperability by multiple vendors complements by creating a complete MAN-LAN solution is optimized for license-exempt LAN operation is optimized for license-exempt and licensed MAN operation Will WiMAX displace WiFi? Wi-fi and WiMax Together WiMAX will not replace WiFi completely, but work TOGETHER Intel is currently integrating WiMAX and WiFi into a single Centrino chip. WiFi s primary role will always be autonomous hotspot service areas (indoor and outdoor 0 ft. < cell radii <500 ft.). WiMax will ultimately replace WiFi in large-scale (greater than 1mi.Sq.) commercial and public roles