Tower station - can provide coverage to a very large area up to 8,000 sqkm.
- connected to ISP through high bandwidth connectivity (example :T3)
- can connect to another tower through microwave link (backhaul).
- allows coverage of the remote areas.
Receiver station -The receiver and antenna could be in a outdoor unit.
Type of service :
LOS :- fixed dish antenna points to WiMAX tower.
- connection is stronger & stable hence more data throughput.
- less interference.
- higher frequency (66GHz) and bandwidth.
8/9/2007 NLOS :-Small subscriber antenna connects to tower (WiFi type service) -Lower frequency range of operation (2-11GHz) -lower radio frequency transmission is unaffected by physical obstructions and are able to bend around the obstacles
8/9/2007 PAN LAN MAN WAN IEEE 802.15 Bluetooth ETSI HiperPAN IEEE 802.11 Wireless LAN ETSI HiperLAN IEEE 802.16 Wireless MAN ETSI HiperMAN IEEE 802.16 e IEEE 802.20 (proposed) 3GPP EDGE (GSM) Wireless Technologies – IEEE Standards IEEE 802.21 30 foot radius 300 foot radius 30 mile radius IEEE 802.15.4 ZigBEE
8/9/2007 Cellular Network Evolution..Contnd Technology 1G 2G 2.5G 3G 4G Design Began 1970 1980 1985 1990 2000 Implementation 1984 1991 1999 2002 2010 Services Analog voice, synchronous data to 9.6 kbps Digital voice, Short messages Higher capacity, packetized data Higher capacity, Broadband data up to 2Mbps Higher capacity, completely IP oriented, multimedia data Standards AMPS, TACS, NMT, etc. TDMA, CDMA, GSM, PDC GPRS, EDGE, 1xRTT WCDMA, cmda2000 OFDM, UWB Data Bandwidth 1.9 kbps 14.4 kbps 384 kbps 2 Mbps 10 Mbps - 20 Mbps Multiplexing FDMA TDMA, CDMA TDMA, CDMA CDMA FDMA, TDMA, CDMA Core Network PSTN PSTN PSTN, Packet network Packet Network All-IP Networks
8/9/2007 Comparison of Cellular & WiMAX Technologies Cellular WiMAX Metric EDGE HSDPA 1 X EVDO 802.16-2004 802.16E Technology Family & Modulation TDMA,GMSK & 8-PSK WCDMA(5MHz),QPSK,16QAM CDMA 2K QPSK & 16QAM OFDM/OFDMA QPSK, 16QAM & 64QAM Scalable OFDMA QPSK,16QAM& 64QAM Peak Data Rate 473Kbps 10.8 Mbps 2.4Mbps 75Mbps(20MHz channel); 18Mbps( 5MHz channel) 75Mbps (max) Average user throughput T-Put <130Kbps <750Kbps initially <140Kbps 1-3Mbps 80% performance of fixed usage model Range Outdoor (average cell) 2-10Km 2-10Km 2-10Km 2-10Km 2-7Km Channel BW 200KHz 5MHz 1.25MHz Scalable:1.5-20MHz Scalable:1.5-20MHz
8/9/2007 2-11GHz 10-66GHz 2.4GHz 5.8GHz 2.4GHz 2.46GHz Assigned Spectrum IEEE 802.20 standard: Global Area Network- the final step in area network. This network would have enough bandwidth to offer Internet access comparable to cable modem service, but it would be accessible to mobile, always-connected devices like laptops or next-generation cell phones. upcoming No No No No No Support for full mobility yes Yes No No No No Adaptive Modulation OFDM QAM, PSK OFDM OFDM Frequency hopping, Direct Sequence Frequency hopping, Direct Sequence Modulation system TCP/IP,ATM TCP,ATM Ethernet Ethernet Ethernet Ethernet Transport protocol supported PTMP, PTCM, Mesh PTP,PTCM PTMP PTMP PTMP Point To Multi-Point (PTMP) Network architecture supported Several miles More than a mile 200yards 200yards 200yards 200yards Propagation distance 70Mbps 54Mbps 54Mbps 11Mbps 2Mbps Max throughput 802.16a 802.16 802.11g 802.11a 802.11b 802.11 Feature Wireless Broadband Metrics
High-speed digital signal is divided into multiple lower speed sub channels that are independent from each other and modulated separately on evenly spaced sub carriers using Fast Fourier Transform (FFT) processors.
This method reduces effects of Multi-path fading, Delay Spread for lower frequencies.
Lower transmission power for low-data-rates.
The missing bits from one channel can be transmitted on other channels and the signal is retrieved.
OFDM-spread spectrum scheme is used for digital TV and digital audio broadcasting and wireless networking (IEEE 802.11a/g)
OFDM system must employ TDMA/FDMA technique to accommodate multiple users; OFDM-256 FFT mode is proposed for IEEE 802.16d (WiMAX fixed-service).
RF Channel One user Sub carriers Lost bits received from other sub channels
8/9/2007 Serial To Parallel Random Data Generator Modula tion Mapping IFFT Guard Period (Cyclic Prefix) Insertion Parallel To Serial Channel Serial To Parallel Guard Period Removel FFT Demodulation Parallel To Serial OFDM Transceiver Block Schematic
8/9/2007 Insertion of Cyclic Prefix (CP) to mitigate ISI
Inter Symbol Interference (ISI) can be eliminated if CP period is greater than channel delay spread.
CP is a repetition of last samples of data portion of the block that is appended to the data payload. This prevents inter-block interference and less complex equalization at the receiver end.
But it is an overhead which reduces the bandwidth efficiency.
8/9/2007 OFDM Technique Transmitted Signal Spectrum Received Signal Spectrum Frequency Single Carrier Mode Level S1 S2 S3 S4 S5 Time Serial Symbol stream used to modulate a single-wide band carrier Symbols have narrow frequency and long symbol time S1 S2 S3 S4 S5 Each of the symbols used to modulate a separate carrier. Orthogonal Frequency Division multiplexing Mode Frequency Frequency Orthogonal Frequency Division multiplexing Mode The light background is transmitted spectrum and the orange portion is received spectrum Frequency Level Single Carrier Mode
8/9/2007 Effect of Sub-channelisation Transmitted DOWN stream of OFDM Spectrum from BS where each slot is a RF carrier Transmitted UP stream of OFDM Spectrum from SS, all the carriers are transmitted but at a ¼ level that transmitted by BS, hence the range is less . Transmitted UP stream of OFDM Spectrum from SS, only ¼ the carriers are transmitted but at same level as transmitted by BS, and hence ¼ the capacity .
Sub-channelisation is optional in Upstream in WiMAX.
Sub –channelisation will enable balanced link budget such that system gain is similar to both uplink & down link.
8/9/2007 Orthogonal Frequency Division Multi-Access (OFDMA)
OFDMA is a multi-user OFDM technique.
WiMAX radio channel is divided into multiple sub carriers and dynamically assigned to multiple users so that sub carrier-group sub channels can be mapped to each user.
Mitigates problems due to fading and interference based on the location and propagation characteristics of each user.
Data rates provided to each user can be varied dynamically based on the number of sub carriers assigned to the user using varying size Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) processors.
OFDMA 128/512/1024/2048 FFT Modes have been proposed for Channel Bandwidths of 1.25/5/10/20MHz respectively in IEEE 802.16e standard (mobile service).
For example, OFDMA 1024 FFT is used in Korea’s WiBRO.
Assign sub carriers as needed OFDMA Modulator OFDM De-Modulator OFDM De-Modulator OFDM De-Modulator Split into sub carriers RF Channel Multi- user Sub carriers
8/9/2007 OFDMA Parameters of a typical WiMAX System S.No OFDMA Parameter Value 1 System Channel Bandwidth (in MHz) 10 2 Sampling Frequency (Fp in MHz) 11.2 3 FFT Size (Nfft) 1024 4 Sub-carrier Frequency Spacing (in KHz) 10.94 5 Useful Symbol Time (Tb = 1/f) (in μ sec ) 91.4 6 Guard Time (Tg = Tb/8) (in μ sec ) 11.4 7 OFDMA Symbol Duration (Ts = Tb + Tg) (in μ sec ) 102.9 8 Frame Duration (in milli seconds) 5 9 No of OFDMA symbols 48 10 Down Link PUSC [Null Carriers] 184 Down Link PUSC [Pilot Sub-Carriers] 120 Down Link PUSC [Data Sub- Carriers] 720 Down Link PUSC [Sub -Channels] 30 11 Up Link PUSC [Null Carriers] 184 Up Link PUSC [Pilot Sub-Carriers] 280 Up Link PUSC [Data Sub- Carriers] 560 Up Link PUSC [Sub -Channels] 35
8/9/2007 Up to 17Mbps Up to 33 Mbps Up to 75 Mbps BPSK QPSK BPSK QPSK 16 QAM BPSK QPSK,16 QAM,QAM,64QAM, 256 QAM BPSK QPSK 16 QAM, 64 QAM Max Data Rate Up to 50Km (LoS) Upto 8Km (Near LoS) WiMAX Carrier Serving Area The area of coverage depends on RF Channel Bandwidth of the carrier and the modulation scheme (BPSK,QPSK,16QAM,64QAM) used. (more details in Section: WiMAX NLOS Coverage and Capacity ) For a 20MHz RFcarrier bandwidth and 64QAM modulation scheme and 3Km distance from Base Station, the Data carrying capacity is 75Mbps.
WiMAX Multi-Antenna Implementation 8/9/2007 Matrix A Matrix B ( Space-Time Block coding) ( Spatial Multiplexing) MIMO (Multiple Input-Multiple Output) Open Loop MIMO Closed Loop MIMO Beam forming (Transmitter Adaptive Antenna)
Open loop MIMO : The Communication channel does not utilize the information of propagation channel.
MATRIX A MIMO : A single data stream is replicated and transmitted over multiple antennas.
The redundant data streams are each encoded using mathematical algorithms known as Space-Time Block codes so that the transmitted signal is orthogonal to the rest reducing self-interference and increases receiver’s capability in distinguishing the signals and extends coverage .
MATRIX B MIMO : The signal to be transmitted is split into multiple data streams and is transmitted from a different BS transmit antenna operating in the same time –frequency resource allocated for the receiver. The receiver distinguishes the actual and multipath signal by employing diversity techniques.
MATRIX B MIMO technique increases channel capacity.
WiMAX Multi-antenna implementation …. Contnd
8/9/2007 Serial to Parallel Converter TX Diversity Coding [S0, -S1*] [S1, -S0*] (Alamouti Coding) IFFT IFFT DAC/ RF DAC/ RF Diversity Techniques at TX & RX in WiMAX Rx Tx1 Tx2
X is the output of the encoder and S0,S1 are input symbols into the encoder. * is complex conjugate of the symbol.
The rows of the matrix represent Tx antennas and columns the time. Each element of the matrix indicates which symbol is to be transmitted from which antenna and when.
Maximum Ratio Combining : Combines the outputs of all the antennas to maximize the received signal energy to noise ratio.
RF/ ADC FFT Diversity Combining S0 -S1* S1 -S0* Time Tx Antennas X =
8/9/2007 MIMO Matrix A & B operation The receive signals can be expressed as : RX1(f)= (H1,1(f) x TX1)+ (H2,1(f) x TX2) RX2(f) =(H2,2(f) x TX2) + (H2,1(f)x TX1) MIMO Matrix A
The Code works with a pair of symbols such that they are transmitted in two time slots from two antennas.
The Data rate is same as that enters the encoder.
MIMO Matrix A techniques improve the coverage area.
MIMO Matrix B S0 S1
The Code works with a pair of symbols such that they are transmitted in one time slot from two antennas.
The Data rate is DOUBLE as that enters the encoder.
MIMO Matrix B techniques improve the capacity of the system.
TX1 TX2 RX1 RX2 H1,1 (f) H2,1 (f) H2,2 (f) H1,2 (f) S0 -S1* S1 -S0* Time Tx Antennas X = TX1 TX2 RX1 RX2 H1,1 (f) H2,1 (f) H2,2 (f) H1,2 (f) Tx Antennas Time X =
8/9/2007 AirSpan’s 16e USB mobile device AirSpan’s EasyST 4 X 90 ○ antennas built into the vertical cone Source: AirSpan Wimax Product Datasheet
8/9/2007 BS Beam Forming Technique (Adaptive Antenna System) SS SS F1 F1 F1 Beam forming (AAS): Channel information is conveyed from WiMAX CPE to the WiMAX BS. Based on the info, the BS utilizes signal processing techniques to calculate weights to be assigned to the transmitter controlling the phase and amplitude of the signal. Then the optimal radiation pattern is steered into the direction for communication SS
Leasing backhaul facilities from Carrier Telecom Companies is cost prohibitive.
WiMAX provides Point-to-Point links up to 30miles (50Km) ,with data rates capable of supporting multiple E1/T1s.
Cellular Operators can use WiMAX equipment to backhaul Base Station traffic to their Network Operating and Switching Centers.
Based on the availability of spectrum for WiMAX in different countries, cellular backhaul application may or may not cover nation wide coverage.
Wired solutions to provide backhaul in rural and sub-urban areas is not cost effective.
DSL or other cable technologies cannot give sufficient bandwidth for cellular backhaul, particularly for upcoming 3G networks.
WiMAX is the obviously advantageous .
8/9/2007 WiMAX in Private Networks (1) For Cellular Back haul Subscriber Station Subscriber Station NOC & Switching center Cell Site Cell Site Base Station WiMAX network Internet PSTN
8/9/2007 WiMAX in Private Networks (2) For Wireless Service Provider (WSP) Backhaul.
Advantage of WiMAX for Wireless Service Provider (WSP)
If the access network uses Wi fi equipment , the overall WSP network is referred to as Hot Zone.
As WSPs typically offer voice,data and video, the built in feature of WiMAX will help prioritize and optimize the backhaul traffic.
WiMAX equipment can be deployed quickly, facilitating a rapid rollout of the WSP Network.
WiMAX is the obviously advantageous to WSPs
Base Station Subscriber Station Wi Fi Hotspot WiMAX Access Network Internet PSTN WiMAX backhaul Subscriber Station Video
8/9/2007 WiMAX in Private Networks (3) For Banking Network.
Advantage of WiMAX for Banking Networks
WiMAX data encryption offers excellent link security.
Broad coverage and high capacity allows Banks regional office to be connected to Branch office and ATMs
WiMAX offers high degree of scalability of traffic.
WiMAX QoS is used to prioritize voice (telephony among branches), data (financial transactions,email,internet & intranet) and video (Surveillance,CCTV) traffic.
WiMAX is obviously advantageous to banking networks
Regional office BS ATM surveillance VoIP phones SS WiMAX network Branch office SS surveillance Internet PSTN
8/9/2007 School Board office BS SS Distance education WiMAX network VoIP phones LAN Distance education Instructor School A School B WiMAX in Private Networks (4) For Education Network.
Advantage of WiMAX for Education Networks
School boards use WiMAX networks to connect school & board offices with in a district.
Key requirements for a school system are NLOS, high bandwidth (>15Mbps),PTP & PTMP capability and large coverage footprint.
WiMAX QoS can deliver full range of communication requirements, including telephony voice, Internet & intranet access data) and distance education video) between school board office & all schools in the district.
WiMAX is obviously advantageous to Education networks
VoIP phones SS LAN students Internet PSTN students
8/9/2007 WiMAX in Private Networks (5) For Public Safety Network. Dispatch LAN Server Ambulance Police Disaster recovery Fire Services Control Center/ Head Office Admin Terminals
Advantage of WiMAX for Public Safety Network
Public safety agencies like Fire,Police,Search & Rescue can benefit from WiMAX networks.
In addition to two-way radio between dispatch and on-site emergency response team, the WiMAX network can relay video images and data.
This data can be relayed to the expert teams of medical or emergency staff, who can analyze the situation in real-time.
WiMAX takes over the advantage over wireline networks in emergency situation, which require access to information while on the move.
WiMAX is obviously advantageous to Public Safety Networks
8/9/2007 WiMAX in Private Networks (6) For Off-shore Communication
Advantage of WiMAX for Off-Shore Communication
Oil & Gas producers can benefit from WiMAX with communication links between land-based facilities to Oil rigs and platforms.
Remote operations include remote trouble shooting of complex equipment problems, site monitoring and data base access.
Basic communication includes voice telephony, email, internet access and video conferencing.
As facilities are in the off-shore and oil rigs are temporarily located and moved with in the oil or gas field, WiMAX is better solution than over wired solutions.
WiMAX is obviously advantageous to Off-Shore Communication
Internet PSTN Service Boats Operator Laptop Surveillance Camera Drilling Platform Surveillance Camera Drilling Operators Drilling Platform Off-Shore On- Shore SS SS BS
WiMAX in Public Networks (1) In Wireless Service Provider (WSP) Access Network.
Advantage of WiMAX for WSP Access Network
Wireless Service Providers use WiMAX network to provide connectivity to both residential (voice, data & video) and business (voice & internet) customers
WiMAX built-in QoS mechanism is highly suited for mix of traffic carried by WSP.
WiMAX QoS MAC supports multi-level services rendering a common network platform, offering voice, data& video to end customer.
Cellular Operators who have customer base can expand their market presence with WiMAX deployment.
WiMAX is obviously advantageous in WSP access network.
WiMAX implemented by Unwired in Australia with 200 BS in 1200Sq Km with 25000 subscriber base.
8/9/2007 Internet PSTN BS VoIP phones SS LAN students SS surveillance Residential Business/Manufacturer/SOHO/ School/University Internet Cafe VoIP phone Video Services Video Services
8/9/2007 WiMAX in Public Networks (2) For Rural Connectivity.
Advantage of WiMAX in Rural Connectivity
Service Providers can deploy WiMAX to deliver services to under-served markets in rural and sub-urban areas where there is little or no infrastructure is available.
Since WiMAX provides an extended coverage, it is a cost –effective solution than a wireline solution, in delivering services in sparsely populated areas and also helps to improve their local economies.
WiMAX is obviously advantageous in Rural Connectivity.
Internet PSTN BS SS SS VoIP Phone surveillance Business Institute SS LAN Rural Community
8/9/2007 SNMP Management VLAN APPLICATIONS IN WiMAX Office Building Subscriber 2 WiMAX BS VLAN 230 VLAN 231 VLAN 230 VLAN 231 MDU VLAN 10 VLAN 11 VLAN12 Subscriber 1 Subscriber n WiMAX FWA Sector WiMAX FWA Sector WiMAX SS WiMAX SS VLAN Switch (Port based switching on subscriber) VLAN 230 Private Network VoIP Service Provider Core Network Element Manager VLAN 10 VLAN 10 & 11 802.1Q VLAN Aware L2 Switch VLAN 45 VLAN 21 VLAN 230 VLAN 45 VLAN 11 VLAN 21
BASE STATION 8/9/2007 ABS4000 symmetryOne airlink™ Base station of SR Telecom PHY Layer Characteristics
symmetry Base Station
Supports both 1MHz & WiMAX sectors
Consists of (1) RF subsystem (on the tower). (2) Digital subsystem.
Digital subsystem consists of circuit packs meant for dedicated interface to backhaul network, air link processing, voice & data processing and NMS.
RF subsystem consists of circuit packs and antenna components for analog signal processing.
Communication between RF subsystem & digital subsystem is through a digital base band signal carried over optical fiber interface.
Air Interface 802.16-2004 (s/w upgradeable to 802.16e) Frequency Range 1.5GHz FDD(1427-1517MHz);2.3GHz FDD(2300-2500MHz) 2.5GHz TDD(2500-2690MHz);2.5GHz FDD(2500-2690MHz) 3.5GHz TDD(3300-3800MHz);3.5GHz FDD(3300-3800MHz) 10.5GHz FDD (10.15-10.65GHz) Channel BW & Peak Sector Capacity (at 64 QAM ¾ coding) (For TDD,capacity =UL + DL traffic). 1.5 FDD : 1.75(6.5Mbps),3.5(13.1Mbps) 2.3 FDD : 1.75(6.5),3(11.2),3.5(13.1),5(18.8),5.5(20.6),6(22.4),7(26.0) 2.5 TDD: 1.25(4.7),2.5(9.4),4.375(16.3),5(18.8),8.75(32.6),10(3.75) 3.5 TDD: 1.75(6.5),3(11.2),5(18.8),7(26.0) 10.5 FDD:3(11.2),5(18.8),7(26.0Mbps) Duplexing FDD (With Half-FDD SS support) TDD RF Access scheme OFDM 256 FFT (Software upgradeable to SOFDMA) Adaptive Modulation 64QAM,16QAM,QPSK,BPSK Max RF Transmit Power 31dBm Antenna Antenna Gain Omni, Sectoral or Panel. Polarization: Vertical or dual slant +/- 45 0 17.5dB (typical) Receiver Sensitivity -101dBm (BPSK ½),-84dBm(1.75MHz channel) (64QAM ¾) Diversity Two-branch TX/RX Polarization diversity & Maximum Ratio Combining (MRC) Space Time Coding Alamouti Coding Forward Error Correction Reed Solomon & Convolution coding (FEC ) rates ½, 2/3 & ¾. Sub-channeling 2,4,8 and 16 channels Sectors Up to 6 Services: Physical port:RJ45 100Base-T per WiMAX sector Network Interface for voice : VoIP over 100Base-T Network Segmentation : VLAN:IEEE802.1Q/802.1D(802.1p) Convergence Sub layer : Ethernet 802.3 & IP over Ethernet service Packet Switching :Layer-2 switching enables easy internetworking with routers,gateways,firewall,IP phones & PBX,media gateways,Wi-fi base stations,IPDSLAM.
8/9/2007 Circuit Pack of symmetry™ Base Station
BS Circuit pack summary
WSBC: Implements IEEE 802.16 MAC & OFDM PHY layer
WBRU: Provides WiMAX air interface radio for one sector. Each sector has two radios providing diversity
TIF: Provides interface between WBRUs for a sector and digital equipment shelf through fiber optic interface.
SMP: Supports configuration, fault detection and equipment redundancy switching for BS circuit packs.
BCP: Provides synchronization & timing signals to BS Modules generates the network, airlink, system timing for the BS.
ESI: Supplies Interface of the BS circuit pack to External Synchronization Sources such as E1/T1 or GPS.
8/9/2007 ATM Ethernet IP ATM Ethernet IP MAC Convergence Layer (service specific) MAC CPS (Common part sub layer ) Physical Layer Physical Layer Authenticate Encrypt Data Transfer Session Setup (Parameter Negotiation) Polling Access Requests Physical WiMAX Protocol Layers RF power Secret Key Secret Key MAC CPS (Common part sub layer) MAC Convergence Layer (service specific) MAC Privacy Layer MAC Privacy Layer RADIO RADIO
8/9/2007 Primary Management (2nd setup) Secondary Management (optional) -DHCP-TFTP-SNMP Transport -User Data WiMAX Connection Types Basic Connection (1 ST setup) -Power Control-Timing BS
The duplex scheme is Usually specified by regulatory bodies, e.g., FCC
Time-Division Duplex (TDD)
Downlink & Uplink time share the same RF channel
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)
8/9/2007 WiMAX Duplex Transmission BS TRANSMIT RECEIVE A) Frequency Division Duplex f1 f2 TRANSMIT RECEIVE B) Time Division Duplex f1 TRANSMIT RECEIVE C) Half -Frequecny Division Duplex(H-FDD) f1 f2
8/9/2007 Implementing Scalable OFDMA in WiMAX PHY Layer Starting with 802.16-2004, there have been extensions to support from 128 up to 2048 FFT points inside an RF channel (called scalable –OFDMA ) to improve efficiency for lower bandwidth channels and improve performance for higher bandwidth channels while keeping sub-carrier spacing to be constant.
IEEE 802.16 MAC – OFDM PHY TDD Frame Structure 8/9/2007 DL Sub frame Frame n-1 pre. Time Adaptive Frame n Frame n+1 UL sub frame FCH DL burst 1 DL burst n UL MAP Broadcast Control msgs ... UL burst 1 UL burst m DL MAP DCD opt. UCD opt. ... DL burst 2 UL TDMA DL TDM pre. pre.
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 802.16 MAC -- CS – Packet Convergence Sub-Layer
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
8/9/2007 Packet PDU (e.g., IP packet, Ethernet Packet) PHSI MAC SDU = CS PDU Payload Header Suppression Index Optional, Depending on upper layer protocol
IEEE 802.16 MAC – Common Part Sub layer – MAC PDU Format 8/9/2007 CRC (optional) MAC PDU payload (optional) Generic MAC Header (6 bytes) LEN msb (3) H T CID msb (8) LEN lsb (8) Generic MAC Header Format (Header Type (HT) = 0) BW Req. Header Format (Header Type (HT) =1) msb lsb E C Type (6 bits) RS v C I EKS (2) RS v HCS (8) CID lsb (8) BW Req. msb (8) H T CID msb (8) BWS Req. lsb (8) E C Type (6 bits) HCS (8) CID lsb (8) HT: Header Type CI: CRC indicator HCS: Header Check Sequence EC: Encryption Control EKS: Encryption Key Sequence Type: Payload type LEN: Length of Packet RSV: reserved. CID :Connection Identifier
IEEE 802.16 MAC -- CPS -- Three Types of MAC PDUs
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
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 802.16 MAC -- CPS – Data Packet Encapsulations 8/9/2007
IEEE 802.16 MAC – CPS – Uplink Service Classes
The SS uses the contention-based BW request opportunities.
WiMAX QoS profiles 8/9/2007 Source: symmetry™ WiMAX Product Summary of S.R.Telecom, Canada. Application rtCBR rtVBR nrtVBR BE Band Width (Kbps) Latency (ms) Jitter (ms) VoIP √ √ 6-87 <150 <10 Video Conference √ √ 128-1500 <150 <10 Interactive Gaming √ √ √ <85 <80 - Streaming Media, VoD √ √ <2000 <250 - Internet Applications √ √ >512 <250 - File and Rich Media Download √ √ >512 <250 - Wi Fi Hot Spot & Internet Café Backhaul √ >1000 <250 - Remote Office/ VPN √ √ >1000 <250 - 1. Latency limit is not enforced by the system for nrtVBR,BE services. Jitter limit is not enforced by the system for nrtVBR, rtVBR, BE services
IEEE 802.16 MAC – CPS – Bandwidth Grant 8/9/2007
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
IEEE 802.16 MAC – CPS – 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
Presented in the GM sub-header on a UGS connection
request a bandwidth req. opportunity for non-UGS services
IEEE 802.16 MAC – CPS -- Contention UL Access 8/9/2007
Two types of Contention based UL slots
Used for new SS to join the system
Requires a long preamble
Used for sending BW req
Collision Detection and Resolution
Detection: SS does not get the expected response in a given time
Resolution: a truncated binary exponential backoff window
The net usable throughput of WiMAX system will depend on
1. Coverage Calculations :
a) On the choice of OFDM parameters
Channel Spacing (dependent on spectrum profile).
Number of FFT points or sub-carriers inside a channel.
Sub-carriers used as pilot channels.
Sub-carriers used as guard channels.
Symbol duration (including guard period)
Modulation & FEC coding rates.
b) On Path Propagation Loss Model used
Erceg Model for Fixed WiMAX, COST231 for Mobile WiMAX
c) Characteristics of the WiMAX System.
System Gain Parameters of Tx,Rx, heights of Antennas as TX, Rx, Receiver Sensitivity of the System
d) Sectorization & Frequency Re-use
No of Sectors in a Cell Site,
No of frequencies that can be used in a cell.
e) Geographic Area to be Covered
2. Capacity Calculations
No of CPEs used
Over Booking Factor
Average Traffic Demand
Fixed -WiMAX Network Design Flow Sequence 8/9/2007 Frequency Band Path loss Model System Gain Link Budget Calculations Modulation/Coding Type Channel Bandwidth Overbooking Factor Average Traffic Demand Cell/Sector range Cell/Sector Capacity Geographic Area Size Network Eqpt Demand Eqpt Prices OPEX CAPEX Economic Results No of CPEs Capacity Demand
8/9/2007 OFDM Parameters Sno OFDM Parameters Value Choice BW=3.5MHz units Choice BW=1.75MHz units 1 Sampling Frequency (Fs) 7/6 (undersampling) or 8/7 (over sampling) x BW 4 MHz 2 MHz 2 Carriers N FFT 256 256 256 3 Data Carriers (Nused) 192 192 192 4 Useful Time (Tb) NFFT /Fs 64 μsec 128 μsec 5 Subcarrier Spacing (Δs) Fs/NFFT 15.625 KHz 7.8125 KHz 6 Guard time/ Useful Symbol time ratio (Tg/Tb) 1/32,1/16,1/8,1/4 1/32 1/32 7 Cyclic Prefix Time (Tg) Tb/32 2 μsec 4 μsec 8 Symbol Time (Ts) Tb+ Tg 66 μsec 132 μsec 9 Bandwidth Efficiency [(Fs/BW)x(Nused+1)/(NFFT)] 86 % 86 % 10 Total Data channel baud rate (for Nused=192 data carriers)in Kbps (192x (1/Ts) 2909.0909 Kbps 1454.5454 Kbps
Total Data Channel baud rate = 192 * 15.151KBaud = 2.909MBaud
As a large portion of PDU (Physical Data Unit) is allocated for Cyclic Redundancy Check (CRC), Forward Error Correction (FEC), and /or Convolution Coding.
There are two convolution rates per modulation rate yielding 8 different modulation levels as follows:
(1) BPSK ½ (2) BPSK ¾ (3) QPSK ½ (4) QPSK ¾ (5) 16QAM ½ (6) 16QAM ¾
(7) 64QAM 2/3 (8) 64QAM ¾
½, 2/3 and ¾ refer to the fraction of the PDUs allocated for actual user data; the rest is management, CRC bits
Net usable throughput for 3.5MHz RF channel for various modulation scheme is as follows:
For BPSK ½ : 2.909 Mbps x ½ = 1.45 Mbps For 16QAM ½ : 11.636 X ½ = 5.82 Mbps
For QPSK ½ : 5.818 Mbps x ½ = 2.909 Mbps For 16QAM ¾ : 11.636 X ¾ = 8.73 Mbps
In practice, bandwidth tends to be lower by 5% to 7% for a general point-to-point link.
WiMAX Throughput Calculation for RF Channels Table :Throughput and Modulation Modulation Type Used Bits /Baud Throughput (Mbps) BPSK 1 2.909 QPSK 2 5.818 16QAM 4 11.636 64QAM 6 17.454
8/9/2007 WiMAX System Link Budget S. no Parameter Units Downlink (Value) Uplink (Value) Remarks 1 Carrier Frequency MHz 2500 2 Duplexing TDD 3 Multiple Access TDMA 4 Modulation adaptive BPSK,QPSK,QPSK,16-QAM,64-QAM 5 Channel Bandwidth (BW) MHz 3.5 3.5 6 Sampling Frequency (8/7 x BW) MHz 4 4 7 Number of Sub channels used EA 0 16 Transmitter Base Station (BS) Subscriber Station (SS) 8 Input power (Pi) dBm 32 23 9 Height of Tx antenna (Htx) meters 30 6 10 Height of Rx antenna (Hrx) meters 6 30 11 Tx antenna gain Gi dBi 17 15 12 Tx feeder loss dB 0 0 Optical fiber medium to connect IDU & ODU at BS 13 Other connector losses dB 4 0 14 EIRP =Tx power +GTx-miscellaneous losses at TX dBm 45 38 Receiver Subscriber Station Base Station 15 Sub channelization Gain (optional in UL) dB 0 12.04 subchannelisation gain = 10xlog(no of sub channels) 16 RX sensitivity (typical for 3.5MHz & BPSK)** dBm -102.59 -114.63 With Subchannelisation gain in Uplink 17 Receiver antenna gain( Gr) dBi 15 17 18 Receiver feeder loss dB 0 4 19 Total System Gain: EIRP+GRx-Rxfeeder loss(-Rx Sensitivity) dB 162.59 165.63 Margins 20 Fade Margin for 99.995% reliability (as per ITU-R P.530 Recommendation) dB 10 10 21 Maximum allowable path loss dB 152.59 155.63 Receiver Sensitivity= -102+SNR(Rx)+10.log(Fs.(Nused/Nfft).(Nsubchannels/16)) ; Nused : 200; Nfft= 256; Nsubchannels:16 by default if no sub channels are used.
A= 20log(4Πd0/λ) where d0 = 100mtrs ξ= (a-b*(Hbs)+ c/(Hbs)) ξ is path-loss exponent Type C terrain is considered for Path Loss Model as example… 8/9/2007 Erceg Path Loss Model ( recommended model by IEEE 802.16 BWA Team) Path Loss (PL)= A + 10ξlog(d/d0)+ΔLf+ΔLh+S for d>d0 (d0 =100mtr) Terrain A [Hilly areas with moderate -to-Heavy tree density] Terrain B [Intermediate Terrain with moderate tree density] Terrain C [Flat terrain with light tree density] a 4.6 4 3.6 b 0.0075 0.0065 0.005 c 12.6 17.1 20 a,b,c are constants representing certain terrain type. d is the distance between Base Station (BS) and Receive antenna (Rx) in meters. Δ Lf = frequency correction term : = 6*log(f/2000); f is frequency in MHz Δ Lh= receive antenna height correction term: = -10.8log(Hss/2) for Terrain A,B; -20log(Hss/2) for Terrain C. S is shadow fading component. (8.2-10.6dB depending on the terrain and tree density type). 8.2 dB for Terrain C
8/9/2007 Calculation of coverage radius using Erceg Model
A = 20log(4Πd0/λ) where d0 = 100mtrs
= 20*LOG(((4*22/7*100)/(300/2500)),10) ; Where λ (meter) = 300/Freq in MHz ; Freq =2500 MHz
ξ ( Path-loss Component) = (a-b*Hbs+ c/Hbs);
= 3.6-(0.005*30)+(20/30) a = 3.6; b= 0.005 ;c = 20 ( for Type ‘C’ terrain )
10ξ Log(d/d0); where d is the Max Radial Distance to be calculated ; d0 =100mtrs
= 10 * 4.1167 *LOG((7.2*1000/100),10) ; for d = 7.2 Km
ΔLf = 6*log(f/2000); f is frequency in MHz
ΔLh = -20log(Hss/2) for Terrain C.
= -20*LOG(6/2,10) = -9.542425094
S (shadowing Component) = 8.2 dB for Terrain C
Total Path loss (in dB) = A + 10ξlog(d/d0)+ΔLf+ΔLh+S = 156.039 (Max allowable path loss from Link Budget calculation)
P rx= Ptx +Gtx +Grx-connector loss-Total Path loss +Receiver Sensitivity- Fade Margin
= -92.603 dBm [ Receiver Sensitivity for BPSK (-102.692dBm); Fade Margin of 10dB as per ITU-R P.530 ]
For BPSK -1/2 , Maximum Coverage Radius for above set of parameters is 7.2Km
8/9/2007 * Guard Period is taken as 1/32 of Symbol Time for 3.5 MHz RF Channel OFDM-256 in the above calculation NLOS Coverage and Capacity (range limited) at 2.5 GHz Using Erceg Path Loss Model Modulation Coding Rx Sensitivity (for RF Channel 3.5MHz) Max Bit rate (Mbps) * Max radial distance of coverage (in Km) Adaptive Modulation Coverage area in a hexagonal cell of radius 7.2Km Coverage % % Capacity in a Sector(in Mbps) BPSK -1/2 1/2 -102.692 1.454 7.20 38.04 28.22 0.410 QPSK-1/2 1/2 -99.693 2.909 6.10 18.10 13.43 0.391 QPSK-3/4 3/4 -97.892 4.363 5.50 34.94 25.93 1.131 16-QAM-1/2 1/2 -92.692 5.818 4.10 8.11 6.02 0.350 16-QAM-3/4 3/4 -90.892 8.727 3.70 13.73 10.19 0.889 64-QAM-2/3 2/3 -86.392 11.636 2.90 4.29 3.18 0.370 64-QAM-3/4 3/4 -84.692 13.09 2.60 17.58 13.04 1.707 Total Coverage Area (in sq km) 134.78 100.00 5.248 Data Throughput in a Sector (Mbps) Base Station Capacity with 3 Sectors (in Mbps) 15.745