1. WiMAX: Broadband Wireless Access
Wireless Networks Fall 2007

2. 802.16 Standards Development
Use wireless links with microwave or millimeter wave radios
10-66 GHz
802.16a extension to 2-11 GHz
Use licensed spectrum (unlicensed too in a)
Metropolitan in scale
Provide public network service to fee-paying customers
Point-to-multipoint architecture with rooftop or tower-mounted antennas
Wireless Networks Fall 2007

3. 802.16 Standards Development
Provide efficient transport of heterogeneous traffic supporting QoS
Capable of broadband transmissions (2-75 Mbps)
Accommodate both continuous and bursty traffic
Mobile extensions: e
Wireless Networks Fall 2007

4. IEEE 802.16 Protocol Architecture
Wireless Networks Fall 2007

5. Protocol Architecture
Physical layer functions:
Encoding/decoding of signals
Preamble generation/removal
Bit transmission/reception
Medium access control layer functions:
On transmission, assemble data into a frame with address and error detection fields
On reception, disassemble frame, and perform address recognition and error detection
Govern access to the wireless transmission medium
Wireless Networks Fall 2007

6. Protocol Architecture
Convergence layer functions:
Encapsulate PDU framing of upper layers into native MAC/PHY frames
Map upper layer’s addresses into addresses
Translate upper layer QoS parameters into native MAC format
Adapt time dependencies of upper layer traffic into equivalent MAC service
Wireless Networks Fall 2007

7. Wireless Networks Fall 2007
IEEE Services
Digital audio/video multicast
Digital telephony
ATM
Internet protocol
Bridged LAN
Back-haul
Frame relay
Wireless Networks Fall 2007

8. Wireless Networks Fall 2007
Burst Profiles
Each subscriber station negotiates a burst profile with the base station
Burst profiles decided based on QoS needs and channel conditions
Harsher environment demands more robust profiles
Favorable environment allows efficient profiles
Wireless Networks Fall 2007

9. Wireless Networks Fall 2007
IEEE Frame Format
Header - protocol control information
Downlink header – used by the base station
Uplink header – used by the subscriber to convey bandwidth management needs to base station
Bandwidth request header – used by subscriber to request additional bandwidth
Payload – either higher-level data or a MAC control message
CRC – error-detecting code
Wireless Networks Fall 2007

10. Physical Layer: Uplink
Stations transmit in in their assigned allocation specified in an initial map
Uplink sub-frame may also contain contention-based allocations for initial system access
Uses a DAMA-TDMA technique
Error correction uses Reed-Solomon codes
Modulation scheme based on QPSK, 16-QAM or 64-QAM
Wireless Networks Fall 2007

11. Physical Layer: Downlink
Continuous downstream mode
For continuous transmission (audio/video)
Simple TDM scheme is used for channel access
Frequency division duplex (FDD)
Burst downstream mode
For bursty transmission (IP-based traffic)
DAMA-TDMA scheme for channel access
FDD with adaptive modulation, frequency shift division duplexing (FSDD), time division duplexing (TDD)
Wireless Networks Fall 2007

12. Medium Access Control (MAC)
Connection-oriented
All services inherently connectionless mapped to a connection
Connections referenced using a 16-bit connection identifier (CID)
Management channels and transport channels for contracted services
Wireless Networks Fall 2007

13. Wireless Networks Fall 2007
Radio Link Control
Power control and paging
Transition among burst profiles
Downlink burst profile change
Subscriber station monitors downlink quality
Requests a new profile
Granted if base station judges possible
Uplink profile change
Base station monitors the uplink signal quality
Specifies the new profile’s usage code when granting subscriber bandwidth in a frame
Wireless Networks Fall 2007

14. Bandwidth Requests & Grants
Two kinds of subscribers
Grant per connection (GPC)
Grant per subscriber (GPSS)
Both classes request bandwidth per connection for QoS guarantees
For GPC, bandwidth explicitly guaranteed to connection
For GPSS, bandwidth aggregated into a single grant for SS
Wireless Networks Fall 2007

15. Wireless Networks Fall 2007
Requesting Bandwidth
Unsolicited grants
No need to request bandwidth for services that generate fixed units of data periodically
Negotiated at connection setup time
Send a bandwidth request MAC packet
Piggyback request within MAC data packet
Polling by base station
Wireless Networks Fall 2007

16. MAC Management Messages
Uplink and downlink channel descriptor
Uplink and downlink access definition
Ranging request and response
Registration request, response and acknowledge
Privacy key management request and response
Dynamic service addition request, response and acknowledge
Wireless Networks Fall 2007

17. MAC Management Messages
Dynamic service change request, response, and acknowledge
Dynamic service deletion request and response
Multicast polling assignment request and response
Downlink data grant type request
ARQ acknowledgment
Wireless Networks Fall 2007